Treatment of thick fine tailings including chemical immobilization, polymer flocculation and dewatering

ABSTRACT

A process for the treatment of thick fine tailings that include constituents of concern (CoCs) and suspended solids is provided. The process includes subjecting the thick fine tailings to treatments including chemical immobilization of the CoCs, polymer flocculation of the suspended solids, and dewatering. The chemical immobilization can include the addition of compounds enabling the insolubilization of the CoCs. Subjecting the thick fine tailings to chemical immobilization and polymer flocculation can facilitate production of a reclamation-ready material, which can enable disposing of the material as part of a permanent aquatic storage structure (PASS).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/079,455, filed Aug. 23, 2018, which is a U.S. National Stage ofInternational Patent Application No. PCT/CA2017/050227, filed Feb. 23,2017, which claims priority to foreign Canadian Patent Application No.CA 2,921,835, filed Feb. 24, 2016, the disclosures of which areincorporated by reference in their entirety.

TECHNICAL FIELD

The technical field generally relates to the treatment of thick finetailings derived from mining operations, such as oil sands mining.

BACKGROUND

Tailings derived from mining operations are often placed in dedicateddisposal ponds for settling. The settling of fine solids from the waterin tailings ponds can be a relatively slow process and can form astratum of thick fine tailings.

Certain techniques have been developed for dewatering thick finetailings. Dewatering of thick fine tailings can include contacting witha flocculant and then depositing the flocculated material onto asub-aerial deposition area where the deposited material can releasewater and eventually dry. Other techniques for treating thick finetailings include addition of gypsum and sand to produce consolidatingtailings.

In the context of dewatering thick fine tailings, there are a number ofchallenges related to processing the material to facilitate efficientreclamation.

SUMMARY

Several implementations of processes and systems for treating thick finetailings, which can be used in the context of forming a permanentaquatic storage structure (PASS), are described herein.

In one implementation, there is provided a process for treating maturefine tailings (MFT) derived from oil sands extraction and includingconstituents of concern (CoC) comprising bitumen, naphthenic acid,arsenic and selenium.

This process includes retrieving MFT from a tailings pond and providingan in-line flow of the MFT. The process further includes adding in-linean aqueous immobilization solution into the in-line flow of MFT andin-line mixing thereof with the MFT, thereby producing a pre-treatedtailings flow. The aqueous immobilization solution includes animmobilization chemical selected from multivalent inorganic salts. Thepre-treated tailings flow includes immobilized bitumen-clay complexescomprising multivalent cations forming cation bridges between negativelycharged bitumen droplets and negatively charged clay particles;insolubilized naphthenic acid; insolubilized arsenic; and insolubilizedselenium.

The process further includes adding in-line an aqueous flocculantsolution into the pre-treated tailings flow to form a flocculatingmaterial; in-line conditioning and transport of the flocculatingmaterial to produce a flocculated material in a water release zone;depositing the flocculated material onto a sub-aerial deposition area,allowing release water to separate from a solids-enriched material; andforming a permanent aquatic storage structure (PASS) for retaining thesolids-enriched material and a water cap. The forming of the PASSincludes forming a consolidating solids-rich lower stratum below thewater cap; and retaining the immobilized bitumen-clay complexes, theinsolubilized naphthenic acid, the insolubilized arsenic and theinsolubilized selenium to inhibit migration of the CoCs into the watercap.

In certain implementations related to in-line addition of an aqueousimmobilization solution, the aqueous immobilization solution can beneutral or acidic. In addition, the immobilization chemical can be fullydissolved in the immobilization solution prior to the in-line additioninto the in-line flow of MFT. In some implementations, the in-lineaddition and the in-line mixing of the immobilization chemical into theMFT are performed at concentration and mixing intensity sufficient tosubstantially inhibit aggregation of multivalent cation hydroxides andpromote charge neutralization between the negatively charged bitumendroplets and the negatively charged clay particles. In this regard, itis noted that dosages and mixing can result in the formation of cationhydroxides, although the process and the immobilization effects are nottailored in accordance with such cation hydroxide formation. The processcan include the use of dosage and mixing that minimize aggregation ofsuch cation hydroxides such that it generally does not add to theimmobilization mechanisms.

The immobilization chemical can include a divalent cation or a trivalentcation. The immobilization chemical can include an aluminum cation, aferric cation, a calcium cation, or a sulphate anion. Alternatively,immobilization chemical can include or consist of gypsum and/or alum. Incertain implementations related to the concentration of theimmobilization chemical, the immobilization chemical can be added in aconcentration below water saturation thereof. The immobilizationchemical can be selected, formulated and/or added in a concentration soas to immobilize substantially all of the bitumen, naphthenic acid,arsenic and selenium present in the MFT, optionally so as to immobilizesubstantially all of the CoCs present in the MFT and further optionallyso as to avoid increasing flocculant dosage more than 20% or more than10% to achieve a same steady-state deposit clay-to-water ratio (CWR) asan equivalent process excluding addition of an immobilization chemical.

Regarding the process step of in-line addition of the aqueous flocculantsolution, the aqueous flocculant solution can include an anionic polymerflocculant, that can be fully dissolved in the aqueous flocculantsolution prior to addition to the pre-treated tailings flow. In someimplementations, the anionic polymer flocculant includes a sodium-basedpolymer flocculant or a calcium-based polyacrylamide-polyacrylateco-polymer with high molecular weight.

Regarding the process step of in-line conditioning of the flocculatingmaterial, this step can consist of pipeline shearing that is managed toincrease a yield strength of the flocculating material to a maximum, andthen decrease the yield strength to achieve the water release zone whileavoiding overshearing.

Regarding PASS implementations, the process can further include managingthe PASS to render the water cap suitable to supporting aquatic life. Insome implementations, the managing includes supplying fresh water intothe water cap, optionally construction and maintenance of reclamationlandforms, optionally comprising shorelines, littoral zones, waterinlets and water outlets. The managing can also include monitoringcomposition of the water cap, and further optionally controlling waterlevels of the water cap. In addition, the process can include providingan intermediate layer of coke in between the water cap and thesolids-rich lower stratum. In other implementations, the depositedsolids-enriched material remains in-place after deposition and forms theconsolidating solids-rich lower stratum of the PASS. Alternatively, thedeposited solids-enriched material is not relocated after deposition.

In another implementation, there is provided a process for treatingthick fine tailings that includes CoCs and suspended solids. Optionally,the thick fine tailings include mature fine tailings derived from oilsands extraction. The process includes subjecting the thick finetailings to chemical immobilization and polymeric flocculation tochemically immobilize the CoCs and polymerically flocculate thesuspended solids, to produce treated thick fine tailings; and dewateringthe treated thick fine tailings. The dewatering thereby produces anaqueous component depleted in the CoCs and the suspended solids; and asolids-enriched component comprising the chemically immobilized CoCs andthe flocculated solids.

Regarding immobilization and flocculation process step, subjecting thethick fine tailings to chemical immobilization and polymericflocculation can include adding an immobilization chemical to the thickfine tailings to produce a pre-treated tailings; and adding a flocculantinto the pre-treated tailings to form a flocculating material.Optionally, the immobilization chemical and the flocculant are addedin-line. Further optionally, the immobilization chemical is added aspart of an aqueous immobilization solution, and the flocculant is addedas part of an aqueous flocculant solution. In some implementations, thechemical immobilization includes insolubilization of dissolved orsoluble CoCs, and optionally formation of cation bridges betweennegatively charged CoCs and negatively charged mineral particles.

Regarding the dewatering process step, the dewatering can includedepositing the treated thick fine tailings onto a sloped sub-aerialbeach. In some implementations, the dewatering includes depositing thetreated thick fine tailings into a pit, such as a mined out pit, whichcan also be called a mine pit.

In certain implementations of the above process, the latter can furtherinclude forming a permanent aquatic storage structure (PASS) forretaining the solids-enriched component. The PASS includes a water cap;and a consolidating solids-rich lower stratum below the water cap andinhibiting migration of the CoCs into the water cap.

In another implementation, there is provided a process for treatingthick fine tailings that includes CoCs and suspended solids. The processincludes subjecting the thick fine tailings to chemical immobilizationto immobilize the CoCs and produce a pre-treated tailings material. Theprocess further includes subjecting the pre-treated tailings material topolymeric flocculation to flocculate the suspended solids and produce aflocculated tailings material; and dewatering the flocculated tailingsmaterial. The dewatering thereby produces an aqueous component depletedin the CoCs and the suspended solids; and a solids-enriched componentcomprising the chemically immobilized CoCs and the flocculated solids.

In another implementation, there is provided a process for treatingthick fine tailings that includes CoCs and suspended solids. The processincludes subjecting the thick fine tailings to polymeric flocculation toflocculate the suspended solids and produce a flocculated tailingsmaterial; and dewatering the flocculated tailings material. Thedewatering thereby produces an aqueous component depleted in thesuspended solids and including CoCs; and a solids-enriched componentcomprising the flocculated solids. The process further includessubjecting the aqueous component to chemical immobilization toimmobilize the CoCs and produce a contaminant-depleted water stream anda contaminant enriched stream including the immobilized CoCs.

In another implementation, there is provided a process for treatingthick fine tailings that includes CoCs and suspended solids. The processincludes subjecting the thick fine tailings to polymeric flocculation toflocculate the suspended solids and produce a flocculated tailingsmaterial; subjecting the flocculated tailings material to chemicalimmobilization to immobilize the CoCs; and dewatering the flocculatedtailings material. The dewatering produces an aqueous component depletedin the CoCs and the suspended solids; and a solids-enriched componentcomprising the chemically immobilized CoCs and the flocculated solids.

In another implementation, there is provided a process for treatingthick fine tailings that includes CoCs and suspended solids. The processincludes simultaneously adding an immobilization chemical and a polymerflocculent into the thick fine tailings, inorder to chemicallyimmobilize the CoCs and polymerically flocculate the suspended solids;and dewatering the thick fine tailings. The dewatering thereby producesan aqueous component depleted in the CoCs and the suspended solids; anda solids-enriched component comprising the chemically immobilized CoCsand the flocculated solids.

In another implementation, there is provided a process for treatingthick fine tailings that includes CoCs and suspended solids. The processincludes adding a polymeric compound to the thick fine tailings. Thepolymeric compound includes multivalent cation groups effecting chemicalimmobilization of the CoCs, and organic polymeric groups effecting thepolymeric flocculation of the suspended solids. The process furtherincludes dewatering the thick fine tailings to produce an aqueouscomponent depleted in the CoCs and the suspended solids; and asolids-enriched component comprising the chemically immobilized CoCs andthe flocculated solids.

In another implementation, there is provided a process for treatingthick fine tailings that includes CoCs comprising surfactants andsoluble metal, metalloid and/or non-metal compounds. The processincludes adding an immobilization chemical into the thick fine tailingsin order to immobilize the CoCs and produce a pre-treated tailings. Thepre-treated tailings include insolubilized surfactants; andinsolubilized metal, metalloid and/or non-metal compounds. The processfurther includes adding a flocculant into the pre-treated tailings toflocculate suspended solids and form a flocculating material;conditioning the flocculating material to produce a flocculatedmaterial; and dewatering the flocculated material. The dewateringproduces an aqueous component depleted in the CoCs and suspended solids;and a solids-enriched component comprising the insolubilizedsurfactants, the insolubilized metal, metalloid and/or non-metalcompounds and the flocculated solids.

In another implementation, there is a process for treating thick finetailings that includes CoCs comprising hydrocarbons, surfactants andsoluble metal, metalloid and/or non-metal compounds. The processincludes adding an immobilization chemical into the thick fine tailingsin order to immobilize the CoCs and produce a pre-treated tailings. Thepre-treated tailings include immobilized hydrocarbon-mineral complexes;insolubilized surfactants; and insolubilized metal, metalloid and/ornon-metal compounds. The process further includes adding a flocculantinto the pre-treated tailings to flocculate suspended solids and form aflocculating material; conditioning the flocculating material to producea flocculated material; and dewatering the flocculated material. Thedewatering produces an aqueous component depleted in the CoCs andsuspended solids; and a solids-enriched component comprising theimmobilized hydrocarbon-mineral complexes, the insolubilizedsurfactants, the insolubilized metal, metalloid and/or non-metalcompounds and the flocculated solids.

In another implementation, there is a process treating thick finetailings that includes CoCs and suspended solids. The process includesadding an aluminum sulphate based compound into the thick fine tailingsin order to immobilize the CoCs and produce a pre-treated tailings. Thealuminum sulphate based compound is added at sufficient dosage andmixing so that aluminum cations form cation bridges between negativelycharged immiscible CoCs and negatively charged clay particles, toproduce immobilized complexes; and insolubilize dissolved CoCs to forminsolubilized CoCs. The process further includes adding an anionicpolyacrylamide based flocculant into the pre-treated tailings toflocculate the suspended solids and form a flocculating material;conditioning the flocculating material to produce a flocculatedmaterial; and dewatering the flocculated material. The dewateringproduces an aqueous component depleted in the CoCs and suspended solids;and a solids-enriched component comprising the immobilized complexes,the insolubilized CoCs, and the flocculated solids.

In another implementation, there is provided a process treating thickfine tailings that includes CoCs and suspended solids. The processincludes adding a calcium sulphate based compound into the thick finetailings in order to immobilize the CoCs and produce a pre-treatedtailings. The calcium sulphate based compound is added at sufficientdosage and mixing so that calcium cations form cation bridges betweennegatively charged immiscible CoCs and negatively charged clayparticles, to produce immobilized complexes; and insolubilize dissolvedCoCs to form insolubilized CoCs. The process further includes adding ananionic polyacrylamide based flocculant into the pre-treated tailings toflocculate the suspended solids and form a flocculating material;conditioning the flocculating material to produce a flocculatedmaterial; and dewatering the flocculated material. The dewateringproduces an aqueous component depleted in the CoCs and suspended solids;and a solids-enriched component comprising the immobilized complexes,the insolubilized CoCs, and the flocculated solids.

In another implementation, there is provided a permanent aquatic storagestructure (PASS) for storing thick fine tailings. The PASS includes acontainment structure defining side walls and a bottom; a water capwithin the containment structure; and a solids-rich lower stratum belowthe water cap. The solids-rich lower stratum includes polymerciallyflocculated solids and immobilized CoCs.

Regarding layering of the PASS, the solids-rich lower stratum can beformed from discharging thick fine tailings pre-treated by chemicalimmobilization and polymer flocculation into the containment structure.Optionally, the solids-rich lower stratum is from a depositedpre-treated material and remains in-place after deposition. In someimplementations, the PASS includes an intermediate layer in between thewater cap and the solids-rich lower stratum. The intermediate layer canbe composed of coarse particulate material, such as coke. The coke canbe derived from a bitumen processing operation.

In implementations related to the immobilized CoCs, the immobilized CoCscan include immobilized bitumen-clay complexes, insolubilized CoCs (suchas insolubilized surfactants and/or insolubilized naphthenic acids,insolubilized arsenic, insolubilized selenium, and/or insolubilizedheavy metals) and can further be selected from divalent and trivalentsalts, including alum, gypsum or both.

In implementations related to the water cap, the PASS can include afresh water line for introducing fresh water into the water cap; and/ora recycle water line for removing recycle water from the water cap. Thewater cap can have a composition suitable to support aquatic life.Optionally, the PASS includes reclamation landforms selected fromshorelines and littoral zones, and/or monitoring systems configured formmonitoring a composition of the water cap.

In another implementation, there is provided a system for treating thickfine tailings comprising CoCs and suspended solids. The system includes:

-   -   a tailings supply pipeline for transporting the thick fine        tailings;    -   an immobilization addition line in fluid communication with the        tailings pipeline for adding an immobilization chemical;    -   a polymer flocculant injector in fluid communication with the        tailings pipeline for injecting a polymer flocculant to produce        a flocculation tailings material;    -   a tailings conditioning pipeline in fluid communication with the        polymer flocculant injector for transporting and conditioning        the flocculation tailings material;    -   a deposition outlet for receiving flocculation tailings material        and depositing the same onto a sub-aerial deposition area; and    -   a containment structure including the sub-aerial deposition area        and configured to contain the flocculation tailings material and        allow formation of a water cap and a solids-rich lower stratum        below the water cap, the solids-rich lower stratum comprising        polymercially flocculated solids and chemically immobilized        CoCs.

In another implementation, there is provided a process for treating finetailings that include CoCs that are water mobile and suspended solids.The process includes adding an immobilization chemical to react with theCoCs and enable immobilization of the same; and adding a polymerflocculant to flocculate the suspended solids. The process furtherincludes producing a treated tailings material; and dewatering thetreated tailings material. The dewatering produces a water component;and a solids-enriched component including the CoCs rendered waterimmobile and flocculated solids.

In implementations related to immobilization and flocculation, theimmobilization chemical can include a divalent cation and/or a trivalentcation, optionally gypsum and/or alum. The immobilization chemical canbe selected to immobilize bitumen by cation bridging with suspendedclays, to immobilize naphthenic acids, to immobilize arsenic, and/or toimmobilize and selenium. The immobilization chemical and the polymerflocculant can be each added in-line, and further optionally each addeddissolved in a corresponding aqueous solution. In addition, theflocculant can include an anionic polymer flocculant, such as asodium-based or a calcium-based polyacrylamide-polyacrylate co-polymerwith high molecular weight.

In implementations related to dewatering, the dewatering can includecontinuously discharging the treated tailings material into a pit toallow an initial water release from the solids-enriched component; andcompressing the solids-enriched component below subsequently depositedtreated tailings and/or a water cap.

In certain implementations of the above process, the latter can furtherinclude forming a permanent aquatic storage structure (PASS), optionallycontained in a mine pit, for retaining the solids-enriched component.The PASS includes a water cap; and a consolidating solids-rich lowerstratum below the water cap and inhibiting migration of the CoCs intothe water cap. The deposited solids-enriched component can remainin-place after deposition and can form the consolidating solids-richlower stratum of the PASS.

Optionally, the process also includes managing the PASS to render thewater cap suitable to supporting aquatic life. The managing can includesupplying fresh water into the water cap; construction and maintenanceof reclamation landforms; monitoring composition of the water cap;and/or controlling water levels of the water cap.

Regarding handling of the treated tailings material, the treatedtailings material can be discharged so that the initial water releaseresults in an initial clay-to-water ratio (CWR) in the solids-enrichedcomponent of at least 0.5, 0.6, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95or 1. The treated tailings material can be discharged sub-aerially, andcan be discharged to avoid overshearing flocs in the treated tailingsmaterial. Optionally, the treated tailings material is deliberatelysheared to improve long term water release from the deposit at theexpense of the initial water release, and further optionally to reach atarget floc size between about 50 μm and about 200 μm to enhance longterm water release. Floc size measurements can be made using variousdevices and techniques, such as a Focused Beam Reflectance Measurement(FBRM) device.

In another implementation, there is provided a process for treatingthick fine tailings. The process includes adding an immobilizationchemical to the thick fine tailings to form a pre-treated material; andsubjecting the pre-treated material to pipeline shear conditioning toform a conditioned pre-treated material. The pipeline shear conditioningis provided such that the conditioned pre-treated material has targetrheological characteristics. The process further includes adding aflocculant to the conditioned pre-treated material to produce aflocculated material; and dewatering the flocculated material.

In certain implementations related to shear conditioning, the pipelineshear conditioning of the process can be performed to modify a yieldstress of the pre-treated material from an initial yield stress up to anupper crest yield stress, and then down to a lower yield stress that isin between the initial yield stress and the upper crest yield stress,such that the conditioned pre-treated material has the lower yieldstress. Optionally, the pipeline shear conditioning is performed so thatthe lower yield stress represents a reduction in the yield stress ofabout 30% to 80% from the upper crest yield stress. Further optionally,the pipeline shear conditioning is performed so that the lower yieldstress is at least about 25 Pa lower than the upper crest yield stress,or between about 10 Pa and about 15 Pa. The pipeline shear conditioningcan also be performed so that the lower yield stress is on a generallyflat plateau of yield stress versus time. In addition, the pipelineshear conditioning can be performed to produce a gel-state pre-treatedmaterial having increased yield stress; and then produce the conditionedpre-treated material having an ungelled state and a decreased yieldstress compared to the gel-state pre-treated material. Optionally, thepipeline shear conditioning is performed such that the conditionedpre-treated material has a turbulent flow regime upon addition of theflocculant thereto. Further optionally, the pipeline shear conditioningis controlled according to shear intensity, shear duration and/or totalshear energy imparted to the pre-treated material.

In certain implementations related to immobilization, adding theimmobilization chemical to the thick fine tailings can be performedin-line via a pipe junction. The immobilization chemical and the thickfine tailings can be supplied through a static mixer to form thepre-treated material; and the pre-treated material can be suppliedthrough a conditioning pipeline in order to impart all of the pipelineshear conditioning to the pre-treated material prior to addition of theflocculant. Optionally, the immobilization chemical includes alum,gypsum, or ferric sulphate.

In another implementation, there is provided a process for treatingthick fine tailings. The process includes adding an acidic solutioncomprising an immobilization chemical to the thick fine tailings havingan initial tailing pH to form a pre-treated material having a reducedpH; and subjecting the pre-treated material to pipeline shearconditioning to form a conditioned pre-treated material. The pipelineshear conditioning is provided such that the conditioned pre-treatedmaterial has at least a target pH that is greater than the reduced pH.The process further includes adding a flocculant to the conditionedpre-treated material to produce a flocculated material; and dewateringthe flocculated material.

In some implementations of the process, adding the acidic solution tothe thick fine tailings is performed in-line via a pipe junction; theimmobilization chemical and the thick fine tailings are supplied througha static mixer to form the pre-treated material; the pre-treatedmaterial is supplied through a conditioning pipeline in order to impartall of the pipeline shear conditioning to the pre-treated material priorto addition of the flocculant.

In certain implementations related to shearing, the pipeline shearconditioning can be performed such that the target pH is at least 7.5 orat least 8. Optionally, the pipeline shear conditioning is performedsuch that the target pH is at least 15%, at least 25%, at least 50%, atleast 75%, or higher, above a lowest pH obtained for the pre-treatedmaterial after addition of the acidic solution. The pipeline shearconditioning can also be performed such that the target pH within 10% ofthe initial tailings pH. The pipeline shear conditioning can further beperformed to achieve the target pH that is based on optimal activity ofthe flocculant.

In certain implementations related to immobilization, the acidicsolution includes sulphuric acid. The immobilization chemical caninclude alum, gypsum, or ferric sulphate. The immobilization chemicalcan be completely dissolved in the acidic solution prior to addition tothe thick fine tailings.

In another implementation, there is provided a process for treatingthick fine tailings. The process includes adding an immobilizationchemical to the thick fine tailings and supplying the same to a mixer toform a pre-treated material. The immobilization chemical dosage isdetermined based on the mixer and density characteristics of the thickfine tailings. The process further includes subjecting the pre-treatedmaterial to pipeline shear conditioning to form a conditionedpre-treated material. The process also includes adding a flocculant tothe conditioned pre-treated material to produce a flocculated material;and dewatering the flocculated material.

In certain implementations of the above process, the immobilizationchemical is added to the thick fine tailings via a pipe junction,optionally a T junction, and the mixer is a static mixer locateddownstream and proximate to the pipe junction. The densitycharacteristics of the thick fine tailings can be measured on-line priorto adding the immobilization chemical, and on-line density measurementsare used to control the immobilization chemical dosage.

In another implementation, there is provided a process for treatingthick fine tailings. The process includes adding an immobilizationchemical to the thick fine tailings to form a pre-treated material; andsubjecting the pre-treated material to shear conditioning to form aconditioned pre-treated material. The process further includes adding aflocculant to the conditioned pre-treated material to produce aflocculating material; and subjecting the flocculating material to shearconditioning to increase floc size up to an upper level and to thenbreak down the flocs and decrease floc size to within a target floc sizerange, thereby forming a conditioned flocculated material. The processalso includes discharging the conditioned flocculated material into apit to enable settling and consolidation of the flocs and separation ofwater to form an upper water cap, thereby forming a permanent aquaticstorage structure (PASS).

In some implementations of the above process, the target floc size rangeis pre-determined based on a minimum settling rate and a maximum settledvolume within the PASS. Optionally, the target floc size range isbetween about 50 microns and about 200 microns. Further optionally, thetarget floc size range is sufficient to provide a minimum settling rateto achieve a clay-to-water ratio (CWR) greater than 0.65 within one yearwithin the PASS; or the target floc size range is tailored to a startingCWR of the thick fine tailings to achieve the CWR greater than 0.65within one year within the PASS.

In certain implementations related to shearing, subjecting theflocculating material to the shear conditioning can consist of pipelineshear conditioning, optionally pipe shear conditioning the flocculatingmaterial in a conditioning pipeline to form the conditioned flocculatedmaterial. Discharging of the conditioned flocculated material into thepit can be performed immediately after exiting the conditioningpipeline.

In certain implementations related to conveyance, the process furtherincludes conveying the conditioned flocculated material from theconditioning pipeline to a discharge location. The conveying can beperformed via a conveyance pipeline fluidly coupled to a downstream endof the conditioning pipeline. The conveyance pipeline can be located ona sloped side of the pit, and/or can be configured and operated suchthat the conditioned flocculated material flows therethrough under anon-turbulent flow regime. Alternatively, the conveyance pipeline can beconfigured and operated such that the conditioned flocculated materialflows therethrough under a laminar flow regime. In addition, theconveying can be performed at shear conditions that are sufficiently lowto substantially maintain flocs size within the target floc size range.

In another implementation, there is provided a process for treatingthick fine tailings. The process includes adding an immobilizationchemical to the thick fine tailings to form a pre-treated material; andsubjecting the pre-treated material to shear conditioning to form aconditioned pre-treated material. The process also includes adding aflocculant to the conditioned pre-treated material to produce aflocculating material; and subjecting the flocculating material to shearconditioning to form a conditioned flocculated material. The processfurther includes conveying the conditioned flocculated material to adischarge location under a non-turbulent flow conditions and under shearrate and energy conditions that are lower than those of the shearconditioning used to form the conditioned flocculated material. Theprocess then includes discharging the conditioned flocculated materialat the discharge location into a pit to enable settling andconsolidation of the flocs and separation of water to form an upperwater cap, thereby forming a permanent aquatic storage structure (PASS).

In certain implementations related to shearing, subjecting theflocculating material to shear conditioning is performed in aconditioning pipeline to increase the yield stress of the flocculatingmaterial to an upper crest and then decrease the yield stress and entera water release zone where water releases from flocs.

In certain implementations related to conveyance, the conveying isperformed via a conveyance pipeline fluidly coupled to a downstream endof the conditioning pipeline. The conveyance pipeline can be located ona sloped side of the pit; and/or can be configured and operated suchthat the conditioned flocculated material flows therethrough under alaminar flow regime. The conveying can be performed at shear conditionsthat are sufficiently low to substantially maintain flocs sizeunchanged. The conveyance pipeline can have a pipe diameter greater thanthat of the conditioning pipeline, and can be operated such that a flowrate therethrough is lower than that of the conditioning pipeline.Optionally, the conveyance pipeline comprises multiple conveyance pipesections arranged in parallel and in fluid communication with theconditioning pipeline. The multiple conveyance pipe sections can supplyrespective discharge units that are positioned for discharging theconditioning flocculated material at different locations in the pit.Optionally, the process can further include relocating the conveyancepipeline as fluid rises within the pit.

In certain implementations related to immobilization and flocculation,the steps of adding the immobilization chemical to the thick finetailings, subjecting the pre-treated material to shear conditioning,adding the flocculant to the conditioned pre-treated material, andsubjecting the flocculating material to shear conditioning are allperformed at locations spaced away from the pit. Alternatively, thesesame steps can be all performed by equipment that is not relocated.

In another implementation, there is provided a process for treatingthick fine tailings. The process includes adding an immobilizationchemical to the thick fine tailings to form a pre-treated material, theimmobilization chemical comprising a ferric cation; and subjecting thepre-treated material to shear conditioning to form a conditionedpre-treated material. The process also includes adding a flocculant tothe conditioned pre-treated material to produce a flocculated material;and discharging the conditioned flocculated material into a pit toenable settling and consolidation of the flocs and separation of waterto form an upper water cap, thereby forming a permanent aquatic storagestructure (PASS). Optionally, the immobilization chemical includesferric sulphate.

In another implementation, there is provided a process for treatingthick fine tailings that includes constituents of concern (CoCs) andsuspended solids. The process includes subjecting the thick finetailings to chemical immobilization and polymeric flocculation tochemically immobilize the CoCs and polymerically flocculate thesuspended solids, to produce treated thick fine tailings. The chemicalimmobilization includes the addition of ferric sulphate. The processfurther includes dewatering the treated thick fine tailings to producean aqueous component depleted in the CoCs and the suspended solids; anda solids-enriched component comprising the chemically immobilized CoCsand the flocculated solids.

In another implementation, there is provided a process for treatingmature fine tailings (MFT) derived from oil sands extraction andincluding constituents of concern (CoCs) comprising bitumen, naphthenicacid, arsenic and selenium. The process includes retrieving MFT from atailings pond; providing an in-line flow of the MFT; adding in-line anaqueous immobilization solution into the in-line flow of MFT and in-linemixing therewith, thereby producing a pre-treated tailings flow. Theaqueous immobilization solution includes an immobilization chemicalcomprising ferric sulphate. The pre-treated tailings flow includesimmobilized bitumen-clay complexes comprising ferric cations formingcation bridges between negatively charged bitumen droplets andnegatively charged clay particles; insolubilized naphthenic acid;insolubilized arsenic; and insolubilized selenium. The process furtherincludes adding in-line an aqueous flocculant solution into thepre-treated tailings flow to form a flocculating material; and in-lineconditioning of the flocculating material to produce a flocculatedmaterial in a water release zone. The process also includes dischargingthe flocculated material into a pit and allowing release water toseparate from a solids-enriched material. The process additionallyincludes forming a permanent aquatic storage structure (PASS) in the pitfor retaining the solids-enriched material and a water cap. Thesolids-enriched material forms a consolidating solids-rich lower stratumbelow the water cap; and retains the immobilized bitumen-clay complexes,the insolubilized naphthenic acid, the insolubilized arsenic and theinsolubilized selenium to inhibit migration of the CoCs into the watercap.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1a and 1b are flow diagrams of examples of thick fine tailingsdewatering operations.

FIGS. 2a to 2e are flow diagrams illustrating optional examples of thickfine tailings dewatering operations.

FIG. 3 is a graph of relative removal efficiency of different CoCs fromMFT release water by using different chemicals.

FIGS. 4a and 4b are graphs of removal percentage versus alumconcentration for different CoCs.

FIG. 5 is a graph of release water conductivity and calciumconcentration versus alum concentration.

FIGS. 6a and 6b are graphs of removal percentage versus gypsumconcentration for different CoCs.

FIG. 7 is a graph of release water conductivity and calciumconcentration versus gypsum concentration.

FIGS. 8a to 8c are graphs of polymer flocculant dosage versus alumdosage for the three aPAMs showing CWR responses.

FIG. 9a is a graph of 25 hour CWR versus alum concentration for thethree aPAMs; and FIG. 9b is a graph of optimum polymer dosage versusalum concentration for the three aPAMs.

FIG. 10a is a graph of 25 hour CWR versus gypsum concentration for thethree aPAMs; and FIG. 10b is a graph of optimum polymer dosage versusgypsum concentration for the three aPAMs.

FIGS. 11a and 11b are graphs of optimum polymer dosage versus mixingspeed for aPAM polymers B and C, with alum addition.

FIGS. 12a and 12b are graphs of polymer flocculant dosage versus gypsumdosage for aPAM polymers B and A respectively.

FIGS. 13a and 13b are graphs of metal concentration (arsenic andselenium) versus percentage of dilution with fresh water to reduceconcentrations below target levels 10 years after PASS landform closure.

FIG. 14 is a graph of naphthenic acid concentration versus percentage ofdilution with fresh water.

FIG. 15 is a graph of hydraulic conductivity versus percentage ofdilution with fresh water.

FIG. 16 is a graph of percentage of bitumen sequestered in tailingsversus immobilization chemical dosage for alum, sulfuric acid and ferricsulphate.

FIG. 17 is a graph of total organic carbon content in release waterversus immobilization chemical dosage for alum, sulfuric acid and ferricsulphate.

FIG. 18 is a graph of arsenic content in release water versusimmobilization chemical dosage for alum, sulfuric acid and ferricsulphate.

FIG. 19 is a graph of selenium content in release water versusimmobilization chemical dosage for alum, sulfuric acid and ferricsulphate.

FIG. 20 is a graph of naphthenic acids content in release water versusimmobilization chemical dosage for alum, sulfuric acid and ferricsulphate.

FIG. 21 is a schematic representation of an in-line operation fromchemical immobilization to discharge into the permanent aquatic storagestructure PASS.

FIG. 22 is a schematic representation of another in-line operationchemical immobilization to discharge into the permanent aquatic storagestructure PASS.

FIG. 23 is a graph of pH versus mixing time for two types of tailingsand mixing speed.

FIG. 24 is a graph of pH versus K_(c) for two types of tailings andmixing speed.

FIG. 25 is a graph of static yield stress versus mixing time for severalimmobilization chemical dosages in MFT with feed CWR of 0.2 and mixingspeed of 425 rpm.

FIG. 26 is a graph of static yield stress versus mixing time for severalimmobilization chemical dosages in MFT with feed CWR of 0.3 and mixingspeed of 425 rpm.

FIG. 27 is a graph of static yield stress versus mixing time for severalmixing speeds.

FIG. 28 is a graph of static yield stress versus K_(c) for severalmixing speeds.

FIG. 29 is a graph of total mixing energy versus flocculant dosage andversus 7-day water clarity for pre-treated (which can be consideredcoagulated for this and other figures) MFT with feed CWR of 0.35 andexposed to a low-shear. The terms “cMFT” or “cTFT” can be consideredshorthand for pre-treated and/or coagulated MFT or TFT, respectively.

FIG. 30 is a graph of total mixing energy versus flocculant dosage andversus 28-day CWR for pre-treated MFT with feed CWR of 0.35 and exposedto a low-shear.

FIG. 31 is a graph of total mixing energy versus flocculant dosage andversus 7-day water clarity for pre-treated MFT with feed CWR of 0.35 andexposed to a high-shear.

FIG. 32 is a graph of total mixing energy versus flocculant dosage andversus 28-day CWR for pre-treated MFT with feed CWR of 0.35 and exposedto a high-shear.

FIG. 33 is a graph of CWR versus settling time for two mixing time ofpre-treated fine tailings.

FIG. 34 is a graph of CWR versus settling time for two feed CWR andthree deposit height.

FIG. 35 is a graph of CWR versus settling time for two polymer dosagesand two shear rates.

FIG. 36 is a graph of CWR versus settling time for two polymer dosagesand two Rates.

FIG. 37 is a graph of CWR versus settling time for two feed CWR and twoRates.

FIG. 38 is a graph of CWR versus settling time for two total energy, twoshear rates and two Rates.

FIG. 39 is a graph of CWR versus settling time for three polymer dosageand three T₅₀.

FIG. 40 is a graph of average floc size versus mixing time (before,during and after polymer injection) for four polymer dosage.

FIG. 41 is a graph of average floc size versus total energy for fourfeed CWR.

FIG. 42 is a graph of CWR versus settling time for two Rates at 0 ppmalum and 1300 g/T polymer.

FIG. 43 is a graph of CWR versus settling time for two Rates at 950 ppmalum and 1400 g/T polymer.

FIG. 44 is a graph of CWR versus settling time for two Rates at 950 ppmalum and 2800 g/T polymer.

FIG. 45 is a graph of column elevation versus CWR for pre-treated andflocculated MFT and for flocculated MFT.

FIG. 46 is a graph of column elevation versus clay percentage on mineralfor pre-treated and flocculated MFT and for flocculated MFT.

DETAILED DESCRIPTION

The techniques described herein relate to the treatment of thick finetailings that include constituents of concern (CoCs) and suspendedsolids. The thick fine tailings can be subjected to treatments includingchemical immobilization of the CoCs, polymer flocculation of thesuspended solids, and dewatering.

The long-term result of treating the tailings can be a permanent aquaticstorage structure (PASS) that includes a water cap suitable forsupporting aquatic life and recreational activities. Techniques aredescribed to facilitate the deposition of treated thick fine tailings ata deposition site that over time becomes the PASS. In someimplementations, the solids separated from water during the dewateringof the thick fine tailings do not need to be relocated, e.g., from adrying area, as can be the case for other known techniques fordewatering thick fine tailings. Rather, the solids remain in place andform the basis of a sedimentary layer of solids at the bottom of thePASS. Previous techniques for treating tailings are known to use polymerflocculation for dewatering a stream of thick fine tailings. However,the PASS technique additionally provides for treating the thick finetailings to provide chemical immobilization of CoCs that would otherwiseremain in or transfer into the water, such that the water layer thatinherently forms over the solid, sedimentary layer has CoCs removedallowing for the water cap to be of such a quality it can supportaquatic life. Although the size of a PASS can vary, in someimplementations the PASS can contain a volume of 100,000,000 to300,000,000 cubic metres and can be approximately 100 metres deep at itsgreatest depth. With a PASS of this scale, flocculated material from thetreated thick fine tailings can be directly deposited onto a sub-aerialdeposition area that is proximate and/or forms part of the PASSfootprint. Within a relatively short period of time following closure ofa mine that is feeding treated thick fine tailings into the PASS, e.g.,10 years, reclamation of the tailings is complete. That is, the solidsare contained in the base of the PASS and CoCs are immobilized withinthe solid layer. The water cap is of a quality to support aquatic lifeand recreational activities.

For example, in the context of oil sands mature fine tailings (MFT) thatinclude CoCs such as dissolved metals, metalloids and/or non-metals,naphthenic acids and bitumen, the chemical immobilization can includethe addition of compounds enabling the insolubilization of the metals,metalloids and/or non-metals, as well as naphthenic acids, in additionto chemical bridging of bitumen droplets with suspended clays. The MFTcan also be subjected to polymer flocculation, which can include theaddition of a polymer flocculant solution followed by pipelineconditioning. The MFT that has been subjected to immobilization andflocculation can then be dewatered. The dewatering can be performed bysupplying the flocculated tailings material to a dewatering deviceand/or a sub-aerial deposition site. While MFT derived from oil sandsextraction operations will be discussed and referred to in herein, itshould be noted that various other contaminant-containing tailings andslurry streams can be treated using techniques described herein.

It should be noted that the term “constituents” in the expression“constituents-of-concern” (CoC) can be considered to include orcorrespond to substances that are considered as “contaminants” bycertain institutions, regulatory bodies, or other organizations, whichcan vary by jurisdiction and by evaluation criteria.

In some implementations, subjecting the thick fine tailings to chemicalimmobilization and polymer flocculation facilitates production of areclamation-ready material, which can enable disposing of the materialas part of a permanent aquatic storage structure (PASS).

Tailings are left over material derived from a mining extractionprocess. Many different types of tailings can be treated using one ormore of the techniques described herein. In some implementations, thetechniques described herein can be used for “thick fine tailings”, wherethick fine tailings mainly include water and fines. The fines are smallsolid particulates having various sizes up to about 44 microns. Thethick fine tailings have a solids content with a fines portionsufficiently high such that the fines tend to remain in suspension inthe water and the material has slow consolidation rates. Moreparticularly, the thick fine tailings can have a ratio of coarseparticles to the fines that is less than or equal to one. The thick finetailings have a fines content sufficiently high such that polymerflocculation of the fines and conditioning of the flocculated materialcan achieve a two-phase material where release water can flow throughand away from the flocs. For example, thick fine tailings can have asolids content between 10 wt % and 45 wt %, and a fines content of atleast 50 wt % on a total solids basis, giving the material a relativelylow sand or coarse solids content. The thick fine tailings can beretrieved from a tailings pond, for example, and can include what iscommonly referred to as “mature fine tailings” (MFT).

MFT refers to a tailings fluid that typically forms as a layer in atailings pond and contains water and an elevated content of fine solidsthat display relatively slow settling rates. For example, when wholetailings (which include coarse solid material, fine solids, and water)or thin fine tailings (which include a relatively low content of finesolids and a high water content) are supplied to a tailings pond, thetailings separate by gravity into different layers over time. The bottomlayer is predominantly coarse material, such as sand, and the top layeris predominantly water. The middle layer is relatively sand depleted,but still has a fair amount of fine solids suspended in the aqueousphase. This middle layer is often referred to as MFT. MFT can be formedfrom various different types of mine tailings that are derived from theprocessing of different types of mined ore. While the formation of MFTtypically takes a fair amount of time (e.g., between 1 and 3 years undergravity settling conditions in the pond) when derived from certain wholetailings supplied from an extraction operation, it should be noted thatMFT and MFT-like materials can be formed more rapidly depending on thecomposition and post-extraction processing of the tailings, which caninclude thickening or other separation steps that can remove a certainamount of coarse solids and/or water prior to supplying the processedtailings to the tailings pond.

In one implementation, the thick fine tailings are first subjected tochemical immobilization, followed by polymer flocculation, and thendewatering to produce a solids-enriched tailings material in which CoCsare immobilized. CoCs can sometimes be referred to as contaminants inthe sense that the presence of certain constituents can be undesirablefor various reasons at certain concentrations, within certain matrices,and/or in certain chemical forms. Various tailings treatments includingchemical immobilization, polymer flocculation and dewatering, aredescribed in further detail below.

Chemical Immobilization

Thick fine tailings can include a number of CoCs depending on the natureof the mined ore and processing techniques used to extract valuablecompounds from the ore. Thick fine tailings can include dissolved CoCs,dispersed CoCs that are immiscible in water, as well as fine suspendedsolids.

For example, thick fine tailings derived from oil sands mining caninclude metals (e.g., heavy metals), polyatomic non-metals (e.g.,selenium), metalloids (e.g., arsenic), surfactants (e.g., naphthenicacids), residual bitumen, as well as other CoCs. The CoCs can exist invarious forms and as part of various compounds in the tailings material.In order to reclaim the thick fine tailings, the CoCs can be treated sothat the eventual landform that includes the treated tailings meetsregulatory requirements.

In some implementations, a process for treating thick fine tailingsincludes immobilization of bitumen; removal of toxicity due tosurfactants, metals, non-metals and/or metalloids; and polymerflocculation of the slurry material to reduce hydraulic conductivity ofthe resultant treated fine tailings landform.

In some implementations, the thick fine tailings can be treated with animmobilization chemical, which can include multivalent cations (e.g.,trivalent or divalent). The multivalent cation can be added as part ofan inorganic salt. The multivalent salts can be added to the thick finetailings pre-dissolved in an aqueous solution, which can be acidic orneutral for example. Various multivalent inorganic salts can be used asimmobilization chemicals. For example, aluminum sulphate (e.g., in acidsolution which can be sulfuric acid), aluminum potassium sulphate, ironsulphate, or chloride or hydrated calcium sulphate (gypsum) can be usedfor chemical immobilization of certain CoCs. For example, the trivalentcation Fe³⁺ can be added as part of iron (III) sulphate Fe₂(SO₄)₃.Addition of ferric sulphate to the thick fine tailings can providecertain advantages, such as lower potential H₂S emissions.

The multivalent cation added to thick fine tailings can perform variousfunctions. One function is that the multivalent cation can form a cationbridge between negatively charged bitumen droplets and negativelycharged clay particles in the fine tailings. This bitumen dropletbridging can help immobilize the bitumen within the solids-enrichedmaterial that is formed after dewatering of the treated tailings.Chemical bridging of bitumen droplets with clays can decrease thepotential for gas bubbles to adsorb onto bitumen and migrate out of thesolids-enriched material; or chemical bridging of bitumen droplets withclays can increase the density and viscosity of the bitumen droplet andprevent upward migration in the deposit through buoyancy effects as thedeposit densifies. Thus, the bitumen can remain immobilized within thesolid material and thus inhibiting its migration into adjacent waterregions.

Another function of the multivalent inorganic salt is to insolubilizecertain CoCs present in the thick fine tailings. For instance,surfactants, metals, non-metals, metalloids and other compounds can bepresent in soluble form in the water of the fine tailings material. Inthick fine tailings derived from oil sands, surfactants such asnaphthenic acids are considered CoCs in terms of water toxicity. Inaddition, compounds such as selenium and arsenic can also be present andsubject to certain regulatory requirements. The addition of themultivalent inorganic salt enables such dissolved CoCs to beprecipitated and to remain insolubilized so that the CoCs cannotre-solubilize. Insolubilization decreases the risk of the CoCs migratingout of the solid material or entering the water column.

In some implementations, chemical immobilization is performed withaddition of a coagulant that destabilizes particles in the thick finetailings through double-layer compression and modifies the pore waterchemistry. In this sense, the immobilization chemical can include or bea coagulant for coagulating CoCs from the thick fine tailings to formcoagulated CoCs. The coagulant can include a multivalent inorganic saltas described above and can include other various conventional coagulantspecies. Chemical immobilization by addition of the coagulant to thethick fine tailings can be performed before, during or afterflocculation as will be further described in relation to FIGS. 2a to 2e, although pre-addition can be a preferred mode of operation in manycases.

Certain chemicals referred to herein can be known as coagulants in thefield of water treatment and can therefore can be referred to as“coagulants” in the present application. However, it should be notedthat such chemicals are used herein for the purpose of immobilization inPASS techniques rather than mere coagulation as would be understood inthe water treatment industry, for example. In this sense, the terms“coagulant” and “immobilization chemical” can be used interchangeably aslong as the coagulant performs the function of immobilization asdescribed in the present application. It should still be noted thatcertain immobilization chemicals described herein can or can not performthe function of coagulation. In some implementations, the so-calledcoagulant is added to the fine tailings in quantities superior to whatis known in the water treatment industry for coagulation, e.g., superiorto 350 ppm, which is used for purpose of mere coagulation rather thanimmobilization. It is noted that in many cases the immobilizationchemical that is added will in effect cause some or substantialcoagulation. It is also noted that immobilization chemicals thatgenerally do not cause coagulation can be used in conjunction with aseparate coagulant chemical that provides coagulation effects.

Immobilization Chemical Addition and Mixing into Thick Fine Tailings

When the immobilization chemical is added upstream prior toflocculation, certain features of the immobilization chemical injectionand the subsequent mixing can be provided for enhancing thepre-treatment (e.g., pre-coagulation) prior to flocculation. Forexample, the immobilization chemical injector, subsequent mixers, aswell as pipeline length and diameter leading up to the flocculantinjector can be designed and provided to ensure a desired immobilizationchemical mixing and coagulation time to facilitate benefits ofpre-coagulation. In some scenarios, the immobilization chemical injectorcan be an in-line addition unit, such as a T or Y pipe junction, and atleast one static mixer can be provided downstream of the immobilizationchemical injector. It should nevertheless be noted that theimmobilization chemical injector can take other forms and havealternative constructions for adding the immobilization chemical. Forexample, the immobilization chemical injector can be configured forinjecting an immobilization chemical solution that includesimmobilization chemical species in solution (e.g., in an aqueousacid-containing solution), and can thus be adapted for liquid-phaseinjection of the immobilization chemical solution into an in-line flowof the thick fine tailings. Alternatively, certain immobilizationchemicals can be added in dry form (e.g., powders) and theimmobilization chemical addition unit can in such cases be designed fordry addition. The immobilization chemical addition unit can include anin-line dynamic mixer (e.g., paddle mixer type) or other types of mixerunits.

In some implementations, immobilization chemical dosage can bedetermined based on various factors, including properties of the thickfine tailings and the configuration of the immobilization chemicaladdition unit and subsequent mixer devices that can be present. Forexample, in some implementations, the immobilization chemical can beadded as an immobilization chemical solution by in-line addition intothe in-line flow of the thick fine tailings followed immediately by amixer, such as a static mixer. Immobilization chemical dosage can bedetermined and provided based on the solids content and/or density ofthe thick fine tailings as well as the given mixer design (e.g., numberand type of static mixers). For example, the mixer effects can bepre-determined in terms of the shear imparted to the immobilizationchemical-tailings mixture, which can depend on thick fine tailingsproperties and other operating parameters, such as flow rate andtemperature of the fluid.

Immobilization chemical dosage determination can take various forms. Forexample, given a particular thick fine tailings density and a givenmixer design, a range of effective immobilization chemical dosages canbe determined along with an optimal immobilization chemical dose. Suchdeterminations can be based in laboratory experiments (e.g., using batchmixers units, such as stirred vessels) and/or small scale pilotexperiments (e.g., small continuous in-line addition and mixing units).In addition, immobilization chemical dispersion targets for dispersingthe immobilization chemical upon addition into the thick fine tailingscan be determined and used to provide an appropriate pipe length anddiameter leading up to the immobilization chemical injector to ensureturbulent flow of the tailings at the immobilization chemical injector.For example, target dispersion shear rates can be tested on laboratoryand/or small-scale units, and the pipeline leading to the immobilizationchemical injector as well as the operating conditions (e.g., flow rate)for larger scale operations can be determined accordingly. For example,should a certain Reynolds Number (Re) of the thick fine tailings flow betargeted for immobilization chemical addition, the pipeline diameter andflow rate can be provided to ensure a minimum turbulence level based ondensity and viscosity of the thick fine tailings to be treated. Once thesystem is operational and the pipeline diameter is fixed, the minimumturbulence level can be achieved by controlling certain operatingvariables, such as flow rate (e.g., regulated by an upstream pump) andpotentially the density and/or viscosity of the thick fine tailings(e.g., regulated by dilution or heating).

In some scenarios, immobilization chemical dosage and dispersionrequirements can be determined in part or primarily based on thick finetailings density and a given mixer design. It should also be noted thatother methods can be used to design the system for immobilizationchemical addition, dispersion and subsequent transportation to theflocculation step. In some implementations, the flow regime of the thickfine tailings is turbulent at the immobilization chemical addition pointand a static mixer is provided just downstream of the immobilizationchemical addition point to produce a thoroughly mixed coagulatingmaterial (which can also be referred to as a pre-treated material ingeneral as coagulation can or cannot be present), which is thentransported via pipeline toward the flocculation step.

Pipeline design, flow rate control and determining properties of thethick fine tailings can be used to achieve a first turbulent flow regimeat the immobilization chemical addition point, while mixer designdownstream of the immobilization chemical addition point can be used toachieve a second turbulent flow regime at that point in the process. Thefirst and second turbulent flow regimes can have different minimumtarget thresholds or target ranges.

It should also be noted that a single immobilization chemical additionpoint or multiple immobilization chemical addition points can be used.Each immobilization chemical addition point can have a subsequent mixerarrangement, and the dosage at each addition point can be determinedbased on the properties of the incoming tailing stream as well as thedownstream mixer design.

Pipelining Pre-Treated Thick Fine Tailings to Flocculation

After addition of the immobilization chemical, a series ofkinetics-limiting reactions occurs between the immobilization chemicaland components of the thick fine tailings. In some implementations,these reactions result in pH and rheology changes in the coagulatingthick fine tailings (which can also be referred to as the pre-treatedTFT) during pipeline transportation. It should be noted that the changesin pH and rheology can further affect the subsequent process steps, inparticular the flocculation stage. Impacts of the mixing intensity on pHand rheology are further discussed below and also described in theexperimentation section.

In terms of pH, when the immobilization chemical is a basic compoundthat is added as part of an acid-containing solution (e.g., alum in asulfuric acid solution), the pH of the resulting immobilizationchemical-tailings mixture can show an initial decrease followed by anincrease as the mixture buffers back to a higher pH. FIGS. 23 and 24illustrate this pH decrease and subsequent increase. Other tests haveshown pH can go down as low as 4.5 or 5 after addition of animmobilization chemical acidic solution.

In some implementations, the pipeline that transports the coagulatingmaterial to flocculation can be configured and operated to impart atleast a target pipe-mixing level to the coagulating material prior toflocculation. For example, the pipeline can be provided with sufficientlength and diameter to impart pipe-shear mixing so that the pH of thematerial has bounced back to a minimum target value or within a targetrange. The target pH bounce-back value can be, for example, the initialpH of the thick fine tailings or a desired pH based on optimal activityof the flocculant. In some scenarios, the target pH bounce-back valuecan be between 7.5 and 8.5. The target pH bounce-back value can also bebased on the lowest pH that is obtained, e.g., a pH increase of 5%, 10%,15%, 20%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, 95% or higher based on thelowest pH value that is obtained from the initial decrease afterimmobilization chemical addition.

In addition, the pipeline transporting the coagulating material can beconfigured in terms of mixing intensity and/or total mixing energyimparted to the material. For example, higher mixing intensities canresult in a more rapid pH decrease followed by a more rapid pH increase(see FIGS. 23 and 24). Thus, the flow rate and pipeline diameter, whichcan impact mixing intensity, can be considered in addition to thepipeline length in order to provide the dimensions and conditions toimpart adequate mixing energy over an adequate time scale to achieve thetarget pH bounce back values when the coagulated material reaches theflocculant injector.

Furthermore, properties of the thick fine tailings (e.g., CWR) can alsobe measured and used to configure the pipeline transporting thecoagulating material. As can be seen in FIG. 23, lower CWR can at somemixing intensities result in more rapid pH decrease and bounce-back,notably at the tested 100 RPM mixing intensity where the pH changes for0.2 CWR were faster compared to 0.35 CWR. Thus, CWR or other properties(e.g., density) of the thick fine tailings can be used to determinedesired pipeline configurations and dimensions to achieve target pHbounce back values.

In some implementations, when the coagulating material is subjected topipeline transportation and pipe-shear based mixing certain rheologicalchanges can occur. For example, pipeline mixing can be performed for asufficient time and under shear conditions that cause the coagulatingmaterial to reach a post gel-stage state, which can reduce polymerflocculant dosage in the subsequent step. More particularly, thepipeline mixing can be conducted to cause the coagulating material toincrease in yield strength and reach a generally gel-like state havinggel-like properties, and then the pipeline mixing can be continued sothat this gel-like material returns to an ungelled state havingslurry-like fluid properties. In this manner, the pipeline mixing can beconducted to ensure adequate progression of thecoagulation/immobilization reactions between the immobilization chemicaland components of the thick fine tailings while avoiding thedifficulties that would occur if the flocculant were mixed with agelled, high yield strength material. In this regard, it should be notedthat gel-like materials have higher yield strength and would be moredifficult to mix with the flocculant. Therefore, adding the flocculantto the coagulated slurry after the gel-like material has been “broken”and the yield strength has decreased significantly, can facilitate rapidand thorough mixing of the flocculant and reduced flocculant dosagerequirements. Imparting sufficient pipeline shear energy to thecoagulating material can be done to achieve such a post gel-stagematerial prior to flocculation. Shear intensity and duration as well astotal mixing energy can be assessed in order to provide a pipelineconfiguration and operating conditions (e.g., pipeline diameter andlength, flow rates, etc.) which can also be based on properties of thematerial (e.g., density, CWR, viscosity, yield strength, etc.).

In some implementations, the pipeline mixing of the coagulating materialcan also be provided to ensure a turbulent flow regime or a targetturbulence level of the coagulated slurry at the flocculant additionpoint. The coagulating material can thus have different flow regimeproperties along the pipeline due to its changing properties. Thepipeline diameter and length as well as the flow rate can be providedsuch that the thick fine tailings have turbulent flow regimes at theimmobilization chemical addition point and at the flocculant additionpoint while the flow regime of the coagulating material at certainpoints in between these two addition points can be non-turbulent orlaminar. In order to provide such flow regime properties, a number offactors can be manipulated including flow rates, pipe sizes (length anddiameters), immobilization chemical mixer type and operation,immobilization chemical dosage, and incoming thick fine tailingsproperties (e.g., viscosity or density, which can be manipulated bypre-dilution, for example).

It should be noted that different flow regimes can be used uponinjection of the immobilization chemical and/or flocculant depending onthe mixing requirements of the corresponding injected chemical at theinitial mixing state. Laminar flow regime can be therefore used forinitial mixing upon injection of certain chemicals.

In an in-line system, it should be noted that timing of the flocculantinjection is related to the distance between the immobilization chemicaland flocculant injection points. The distance between those injectionpoints can also be characterized by the mixing of the pre-treated finetailings between the immobilization chemical and flocculant injectionpoints, in terms of intensity and time. Thus, mixing time and mixingdistance can both be used to assess the impact of mixing on thecoagulating material and the flocculant addition point. As mentionedabove, the immobilization chemical pipeline mixing and the flocculantinjection point can be provided such that the flocculant is added oncethe coagulated material has left a gel-stage and/or experienced pHbounce back. In another example, injecting the polymer flocculantdownstream of the immobilization chemical injection point such thatpipeline mixing is within a critical mixing range can facilitateenhanced flocculation. Critical mixing ranges can be determined foropen-pipe configurations by using various empirical and/or computationalmethods. In addition, in dynamic paddle mixers it has been found thatthe optimum polymer flocculant dosage decreases as the critical mixingconstant (K_(c)) increases (e.g., (K_(c)) of 20 to 12,000). K_(c) valuesdetermined for batch or in-line stirred tank impeller vessels may beused to help predict critical mixing ranges for in-line open-pipeoperations, and Camp Number-based scaling methods can be used.

In some implementations, pre-shearing is performed to enhance uniformshearing within the coagulated tailings before injection of theflocculant. In addition, one or more in-line high-shear static mixer(s)(or other in-line shear devices) can be used to enhance or ensure mixingof the core of the coagulated tailings within the pipe to further reducethe yield stress within the pipe.

In some implementations, the coagulating material is subjected tosufficient mixing (e.g., pipeline shear mixing) to reach a generallystable yield stress plateau after descending from a crest in terms ofits yield stress properties. FIGS. 25 to 28 illustrate example curves ofyield stress evolution for mixing of the immobilizationchemical-tailings mixture. In some scenarios, the mixing is conducted toreach a target yield stress value or range or to reach a target yieldstress reduction based on the maximum or average crest value of yieldstress (e.g., 30% to 80%, 40% to 70%, or 50% to 60% reduction of themaximum or average crest value). For example, as shown in FIG. 25, withalum dosage of 1800 ppm the maximum yield stress is about 25 Pa whichdecreases to a plateau value of about 10 Pa to 12 Pa which represents areduction of 52% to 60% of the maximum.

It should be noted that certain polymer flocculants can be sensitive topH and rheology variation. Consequently, both polymer flocculantconsumption and deposit performance can be impacted by the polymerflocculant injection location downstream of the immobilization chemicalinjection location. In some implementations, timing of the flocculantinjection can be enhanced based on properties including yield strengthand/or pH of the pre-treated thick fine tailings that is subjected toflocculation. Certain enhancement techniques and details related theretowill also be discussed in the experimentation section. It should also benoted that the pipeline transporting the coagulating material can havevarious arrangements, including a single pipeline composed of a seriesof pipe sections or a pipeline network that includes a splitter leadinginto multiple parallel pipelines that can rejoined into a singlepipeline prior to flocculation. Such pipeline networks can be configuredto increase pipeline shear imparted to the material, and can also becontrolled and operated to impart different levels of shear to thematerial when desired. It is also noted that the pipeline can includeone or more shear devices (e.g., static mixer) arranged along its lengthto impart part of the desired shear to the material, and such sheardevices and pipeline can be arranged so that the material can eitherpass through or bypass the shear devices.

Thus, various pipeline configurations can be provided in order toproduce a pre-treated coagulated material that is ready forflocculation. For example, mixing intensity, mixing time, pipelinelength and diameter, immobilization chemical dosage, yield stress of thematerial, and flow rate are relevant interconnected factors that can bemanaged to produce the pre-treated coagulated material having target pH,yield stress and flow regime characteristics at the flocculation point.For in-line systems that include a simple pipeline from theimmobilization chemical mixer to the flocculant injector, pipelinelength and diameter can be designed in view of flow rate and tailingsproperties (notably density) in order to impart pipe shear energy in anintensity and over a time period that enable the target pH, yield stressand flow regime characteristics.

This pipeline can have a single diameter along most or all of itslength, or it can have different diameters at particular locations alongits length to achieve desired effects at certain locations. For example,the pipeline can include a pipe section proximate the immobilizationchemical addition point with a first, relatively small diameter toimpart higher shear rates (i.e., higher shear intensity) to cause asharp pH reduction and/or a sharp yield stress increase at that upstreamlocation. The pipeline can also include a subsequent intermediate pipesection that has a second, larger diameter and a pipe length thatprovide a desired shear energy and residence time for the coagulatingmaterial. This intermediate pipe section can be configured to impart adesired mixing energy and intensity to achieve the desired pH and yieldstress characteristics, but is not necessarily concerned in a directmanner with turbulence or flow regime. Next, the pipeline can include adownstream pipe section that feeds into the flocculant injector, andthis downstream pipe section can have a third, smaller diameter toensure turbulence as the material contacts the flocculant. Thisdownstream pipe section could be relatively short in length as it simplyhas to ramp up the turbulence of the material to a desired level priorto flocculant addition and is not necessarily designed for imparting agiven amount of energy for the pH or yield stress evolution. Variousother pipeline configurations are also possible for achieving desiredpH, yield stress and flow regime characteristics. For example,alternatively, pipe section can be increased to ensure laminar flow.

Flocculation

A polymer flocculant can be added to the fine tailings in order toflocculate suspended solids and facilitate separation of the water fromthe flocculated solids. The polymer flocculant can be selected for thegiven type of fine tailings to be treated and also based on othercriteria. In the case of oil sands MFT, the polymer flocculant can be amedium charge (e.g., 30%) high molecular weight anionic polymer. Thepolymer flocculant can be a polyacrylamide-based polymer, such as apolyacrylamide-polyacrylate co-polymer. The polymer flocculant can havevarious structural and functional features, such as a branchedstructure, shear-resilience, water-release responsiveness to fast-slowmixing, and so on.

It should be noted that polymer flocculant is not limited to a mediumcharge, as altering the pH can influence the charge requirements. Insome implementations, the polymer flocculant charge is selected inaccordance with pH.

In some implementations, the overall flocculation and dewateringoperations can include various techniques described in Canadian patentapplication No. 2,701,317; Canadian patent application No. 2,820,259;Canadian patent application No. 2,820,324; Canadian patent applicationNo. 2,820,660; Canadian patent application No. 2,820,252; Canadianpatent application No. 2,820,267; Canadian patent application No.2,772,053; and/or Canadian patent application No. 2,705,055. Suchtechniques—including those related to flocculant selection; rapiddispersion; pipeline flocculation and water-release condoning; CampNumber-based design and operation; injector design and operation;sub-aerial deposition and handling; pre-shearing; pre-thinning; andpre-screening—can be used or adapted for use with techniques describedherein related to chemical immobilization, polymer flocculation anddewatering. The above documents are incorporated herein by reference. Itshould also be noted that various techniques described in such documentscan be adapted when included with techniques described in the presentapplication, such as chemical immobilization and coagulation as well aspost-flocculation handling, discharging and management.

In some implementations, the polymer flocculant is added as part of anaqueous solution. Alternatively, the polymer flocculant can be added asa powder, a dispersion, an emulsion, or an inverse emulsion. Introducingthe polymer flocculant as part of a liquid stream can facilitate rapiddispersion and mixing of the flocculant into the thick fine tailings.

In some implementations, the polymer flocculant can be injected into thepre-treated thick fine tailings using a polymer flocculant injector. Forexample, static injectors and/or dynamic injectors can be used toperform flocculant addition. The injection can be performed in-line,that is, into the pipeline for example. A length of the pipelinedownstream of the flocculant injection point can be dedicated todispersion of the polymer flocculent into the pre-treated thick finetailings, thereby producing treated thick fine tailings that is readyfor conditioning and eventual dewatering.

As mentioned further above, the incoming pre-treated thick fine tailingsthat has been subjected to coagulation can arrive at the flocculantinjector with certain pH, yield stress, and flow regime characteristicsthat facilitate flocculant dispersion, mixing and reaction withsuspended solids.

Immediately after flocculant injection (e.g., via a co-annular injectorwhere flocculant inlets are spaced away from the pipe side wall and aredistributed around an annular ring through which the pre-treatedtailings flow), there can be a dispersion pipe section that receives theflocculating material and imparts pipe shear energy to the material. Thedispersion pipe length as well as polymer flocculant dosage can beprovided based on various factors, which can include the density and/orclay content of the thick fine tailings as well as the flocculantinjector design. In some scenarios, for a given injector design anddensity of the thick fine tailings, optimum ranges of polymer flocculantdosage and dispersion pipe length can be determined, particularly whenthe target pH, yield stress, and flow regime characteristics have beenprovided. More regarding process modelling will be discussed in furtherdetail in the experimentation section below.

Pipeline Conditioning and Transport after Flocculation

In some implementations, the process includes pipeline conditioning ofthe treated thick fine tailings after flocculant addition anddispersion. The pipeline conditioning can notably be adapted to the typeof dewatering, deposition and disposal that will be conducted (e.g., exsitu dewatering devices, sub-aerial deposition in thin lifts, ordischarging into a pit to form a permanent aquatic storage structure(PASS), as will be discussed in greater detail below). For dewatering bysub-aerial deposition in thin lifts, the pipeline conditioning can beconducted to increase the yield stress of the flocculated material to acrest or maximum where the material presents gel-like characteristics,and then reduce the yield stress and effect floc breakdown to form aflocculated material in a water release zone yet still having relativelylarge flocs. For dewatering within a PASS, the pipeline conditioning canbe modified such that the floc breakdown reduces the flocs to smallersizes that provide settling time and settled volume characteristics forformation of the PASS. The floc size for thin lift dewatering can beprovided to promote rapid initial water release a separation from theflocculated solids, while the floc size for the PASS implementation canbe provided to promote both fast settling time and small settledvolumes. For example, the target floc size for dewatering by sub-aerialdeposition in thin lifts can be greater than about 100 μm, about 150 μm,about 200 μm, or about 250 μm; while the target floc size for dewateringvia the PASS implementation can be between about 50 μm and about 200 μm,between about 50 μm and about 150 μm, or between about 75 μm and about125 μm. The target floc size can be treated as an average floc size forprocess control and measurement. The floc size for the PASSimplementation can be provided in order to balance competing effects ofsettling speed and settled volumes, which will depend on the startingCWR of the thick fine tailings, in order to achieve a CWR of at least0.65 within one year after discharge into the PASS containmentstructure. The target floc size depends on polymer dosage of the thickfine tailings, regardless of the starting CWR. For example, with astarting CWR of about 0.1, the target floc size can be provided toachieve above 80% volume reduction within one year of discharge, whereaswith a starting CWR of about 0.4, the target floc size can be providedto achieve above 32% volume reduction within one year of discharge.

Floc size reduction can be achieved by subjecting the treated thick finetailings to pipeline shear sufficient to break down larger flocs to formsmaller flocs while avoiding over-shearing the material where the flocswould be substantially broken down and the material would generallyreturn to its initial slow settling characteristics. The pipeline shearcan include high shear rates and/or sufficiently small pipe diameters inthe conditioning section. The conditioning pipeline can be configuredand implemented based on pre-determined target values for shear ratesand total shear energy to impart to the material, based for example onempirical and/or modelling information. It should also be noted that thesystem can include monitoring equipment for measuring the approximatefloc size (e.g., in-line, at-line or off-line) so that the conditioningpipeline can be adapted and/or regulated based on the measured floc sizeto provide the shear necessary to be within a target floc size range.

In some implementations, the conditioning pipeline terminates at adischarge point where the treated thick fine tailings are supplied tothe dewatering device or site. In alternative implementations, theconditioning pipeline feeds into a conveyance pipeline that transportsthe treated thick fine tailings to the discharge location under reducedshear conditions. The conditioning and conveyance pipelines can beconfigured together to provide a target total shear energy to thematerial prior to deposition as well as high initial shear (i.e., in theconditioning pipeline) followed by lower shear (i.e., in the conveyancepipeline).

In some implementations, the total shear energy imparted to the treatedthick fine tailings prior to discharge is sufficiently high to reach thetarget floc breakdown and yet within a range to facilitate water clarityand settling characteristics within the PASS. For example, it was foundthat, at optimum polymer dosage an average shear rate within 150 s⁻¹ for30 minutes could be imparted after flocculant addition to coagulatedthick fine tailings. Based on this value, a conditioning and conveyancepipelines can be designed and implemented to operate within thisenvelope. More regarding conveyance will be discussed below.

Water separation from the flocs within the PASS can include severalphysical mechanisms. Settlement can be understood as volume reduction ofthe flocculated material, such that settlement is obtained by settling,consolidation and other volume reduction mechanisms. For example, duringwater separation, settling mechanisms where solid flocs and grains falldownward through the liquid phase can evolve into consolidationmechanisms. Modeling settlement within the PASS can combine variousinput data including settling data, consolidation data and otherwater-separation data.

Conveyance and Discharge of Treated Thick Fine Tailings

As mentioned above, the system can include a conveyance pipeline that issized and configured for imparting a reduced or minimum shear to thematerial from the conditioning pipeline until discharge. This can beparticularly advantageous when the distance from the flocculant injectorto the discharge point is substantial or sufficiently great such thatsimple continuation of the conditioning pipeline would impart excessshear and risk over-shearing the material prior to discharge. Theconveyance pipeline can be provided to have a larger diameter comparedto the conditioning pipeline in order to reduce shear during thistransportation step. Alternatively, the conveyance step can includeother methods or systems that do not necessarily involve increasing pipediameter, such as splitting the flow of treated thick fine tailingscoming from a single conditioning pipeline into multiple conveyancelines and operating the conveyance lines at reduced flow rates, therebyreducing shear imparted to the material prior to discharge.

Flow rate and pipe diameter can be controlled in tandem in order toreduce the shear sufficiently to substantially maintain the floc sizeduring conveyance (i.e., from conditioning to discharge). In somescenarios, the floc size change during conveyance is kept within 150 μmwhile keeping the floc size within 50 μm to 200 μm. Thus, if the initialfloc size prior to conveyance is at the maximum target size of 200 μm,then the maximum floc size change should be 150 μm such that the flocsize upon discharge is at least 50 μm. If the initial floc size issmaller than 200 μm, then the maximum floc size change should be kept ata lower level to ensure a minimum floc size of 50 μm upon discharge.Alternatively, when the initial floc size prior to conveyance is above200 μm, then the floc size change can be greater than 150 μm. Ingeneral, the floc size prior to conveyance and after conveyance can betargeted and the process conditions (e.g., shear conditions) can bemanaged such that the floc size upon discharge is within the desiredrange.

Referring to FIGS. 21 and 22, two potential implementations are shownfor transporting and discharging the treated thick fine tailings into apit.

In a first implementation shown in FIG. 21, the treated thick finetailings is discharged into the containment structure of the PASSdirectly after the pipeline conditioning stage. The discharge section ofthe pipeline is in direct fluid communication with the conditioningsection of the pipeline. In this dewatering scenario, the in-lineinjection of the immobilization chemical (e.g., coagulant) and theflocculant can be located on a buttress, upstream of the conditioningpipeline which can be provided sloping down from the buttress toward thedischarge location. In this scenario, the chemical injection assets(e.g., immobilization chemical injector and flocculant injector) canhave to be relocated repeatedly as the level of the PASS rises withtime, e.g., to maintain the slope of the conditioning section of thepipeline. The treated thick fine tailings are then discharged into thepit of the PASS to allow the flocs to settle and the water to separateand form an upper layer, thereby forming the water cap. Without aconveyance pipeline there can be certain challenges and constraints interms of operation and relocation of the chemical injection units.

In a second implementation, as illustrated in FIG. 22, the treated thickfine tailings are conveyed to the discharge location after the pipelineconditioning stage. The pipeline geometry can be adapted to include aconveyance pipe section or arrangement, which is in fluid communicationwith the conditioning pipeline. In addition, the chemical injectionassets can be provided in a central location that would not requirerelocation as the level of the PASS rises, as opposed to theimplementation of FIG. 21. In addition, the conditioning section of thepipeline can also be located off the buttress, which can enhanceaccessibility and operational aspects of that step. The conditioning canbe performed to condition the flocs and the treated thick fine tailingsto a state where continuing pipeline shear would not have a significantor beneficial impact on the terminal floc sizes or settling behavior ofthe discharged material in the PASS. The flocculated and conditionedthick fine tailings can then be sent to the discharge section of thepipeline, via the conveyance section. The conveyance section of thepipeline can be located on a sloped ramp or earthwork to facilitatedistribution to the discharge section. The presence of a conveyancesection therefore facilitates efficient relocation of system assets overtime (e.g., as only conveyance and discharge assets can have to berelocated) as well as centralization of chemical injection units in moresuitable locations for operation, maintenance, chemical supply, and soon. The conveyance system facilitates stable operation of the chemicaladdition and conditioning steps for reliable production of treated thickfine tailings with desired characteristics, while the low-shearconveyance system provides enhanced adaptability and flexibility fortransporting ready-to-deposit material to a variety of differentdischarge points operating at any given time and different dischargepoints that can change location over time.

In terms of the conveyance method, in an in situ or ex situ dewateringcase, conveyance of the flocculated and conditioned thick fine tailingscan be controlled to maintain the floc size at an optimal value orwithin an optimal range for dewatering until deposition into thecontainment structure of the PASS. For example, lengths and diameters ofthe pipes can be chosen in accordance with various parameters includingthe distance to the discharge section and the attrition resistance ofthe flocs from the treated fine tailings. In addition, the conveyancepipes can be configured, positioned and operated such that no additionalpumping is required to transport the material to the dischargelocations. For example, the conveyance pipes can be positioned on aclopped section of the PASS containment structure having an inclinationsufficient for the material to flow under gravity and remaining headprovided by upstream pumps to the discharge locations.

In terms of discharge methods, in an in situ dewatering case, thetreated thick fine tailings can be discharged continuously into thesubaerial pit over a relatively long period of time (e.g., rise rate ofabout 20 meters per year) with the release water coming to the surfaceand the solids settling to the bottom. The discharge points cansometimes be submerged in the water or within the underlying tailingsdeposit, but the primary discharge method would include discharging thematerial onto the top of the fluid and/or onto a solid earth surfaceproximate to the fluid surface. The discharge should be designed andmanaged to avoid over-shearing or destroying the flocs in order tofacilitate initial high water release and good settling rates. Thus, thedischarge points should not be located at a significant height above asolid surface which could lead to a high-energy impact causingover-shearing.

In some implementations, floating pipe sections with discharge ends canbe used to gain access to underutilized areas of discharge. The floatingcan be equipped with floating devices or can be supported by othermeans.

In an ex situ dewatering case, where the bulk of the water has beenremoved prior to deposition, the discharge method can be modified, suchas distributing the discharge to prevent water pooling and modifying thepipe sections and discharge ends to accommodate higher-solids material.

It should also be understood that similar principles can apply to boththe conveyance section and the discharge section to maintain the flocsize in an optimal range for the desired water release and settlingcharacteristics. For example, the conveyance section can be designed toinclude a plurality of pipes for splitting the flow of treated finetailings coming from the conditioning section. Similarly, the dischargesection can be designed to include a plurality of pipes for splittingthe flow of treated fine tailings coming from the conditioning sectionor the conveyance section.

Dewatering

As mentioned above, various dewatering techniques described in severalCanadian patent applications can be used in the context of thetechniques described herein. It should be noted that the overall processcan include several dewatering steps, which will be discussed in greaterdetail in relation to FIGS. 1a and 1b , for example. In general,dewatering can be done by a solid-liquid separator (SLS) or bysub-aerial deposition/discharge. A combination of SLS and sub-aerialdewatering can also be performed.

Various types of SLS's can be used. For example, belt filters and/orthickeners can be used to separate a solids-depleted water stream from asolids-enriched tailings material, both of which can be subjected tofurther processing after dewatering.

In the case of dewatering by sub-aerial deposition, various dewateringmechanisms can be at work depending on the deposition andpost-deposition handling methods that are used. For instance, thin liftdeposition can promote release water flowing away from the depositedmaterial followed by dewatering by freeze-thaw, evaporation, andpermeation mechanisms. For deposition that is performed to promote theformation of a much thicker lower stratum of treated fine tailings withan upper water cap, the lower stratum can dewater with consolidation asa significant dewatering mechanism. More regarding this will bediscussed in relation to forming and managing the permanent aquaticstorage structure (PASS) for the fine tailings and CoCs.

Characteristics of PASS Landform

In some implementations, as mentioned above, a permanent aquatic storagestructure (PASS) can be built via in situ and/or ex situ dewatering ofthick fine tailings that has been subjected to chemical immobilizationand flocculation. A summary of some characteristics of the PASS landformis provided below.

The containment structure of the PASS can be a former mine pit, whichcan include various in-pit structural features such as benches andin-pit dykes. After closure of a mine pit, preparation of in-pitstructures and landforms (e.g., dykes, dumps, temporary dams, pit walls)can be undertaken. Placement of the treated fine tailings can thenbegin. The treated fine tailings can be discharged in various ways atdifferent stages of forming the PASS. The treated fine tailings can bedischarged within the pit in accordance with tailings management andreclamation considerations. During or after placement of the treatedfine tailings, additional landforms, surface water inlets and outlets,and operational infrastructure can be constructed as part of the overallPASS system.

The PASS can be seen as a type of end pit lake—but how it is formed andits target characteristics are different than a conventional end pitlake. For example, the discharged fine tailings are pre-treated beforedepositing into the landform that will become the end pit lake, toenhance dewatering and stability of the landform. Conventional end pitlakes are formed by placing tailings into the mine pit (i.e., thelandform), capping with water, and treating the water within thelandform. In an oil sands application, a conventional end pit lakedirectly deposits untreated MFT into the landform. In contrast, the PASSis formed from pre-treated material such that the MFT is dewatered atdeposition and the water released from the MFT is pre-treated tochemically immobilize CoCs in the solids layer formed at the base of thePASS. Thus the PASS has several advantages over conventional end pitlakes, such as more consistent immobilization characteristics throughoutthe sediment layer, accelerated dewatering, and mitigation of long-termrisks related to CoCs in the tailings.

In a PASS, the CoCs are immobilized prior to deposition in the landform.Fresh water dilution can be used in the aquatic reclamation process, inaddition to the chemical immobilization of CoCs in the sedimentarylayer. Note that fresh water dilution, meaning dilution of the alreadypresent pre-treated water cap, is different than relying on a freshwater cap to overlay fluid fine tails that were deposited untreated intothe landform (i.e., as in a conventional end pit lake). The PASS in areclaimed state will have no persistent turbidity, no (or negligible)bitumen in the water cap and toxicity and metals below guidelinesrequired to support aquatic life. By contrast, a conventional end pitlake uses a fresh water cap and microbial activity as the aquaticreclamation process, and steps are not taken specifically to removebitumen from water released from the fine tailings. A conventional endpit lake will have low persistent turbidity.

Process Implementations

Referring to FIGS. 1a to 1b , there are two main process implementationsparticularly in terms of the dewatering of the flocculated tailingsmaterial. FIG. 1a illustrates an in situ process where the dewateringincludes depositing the flocculated tailings material onto a dedicateddisposal area and optionally forming a permanent aquatic storagestructure (PASS), while FIG. 1b illustrates an ex situ process whereinthe dewatering includes supplying the flocculated tailings material tosolid-liquid separator (SLS).

The processes illustrated in FIGS. 1a and 1b have several commonelements. The thick fine tailings (e.g., MFT) 20 is retrieved from atailings pond 22 and supplied by pipeline to various processing units.An immobilization chemical 24 is added to the MFT stream 20 to produce apre-treated tailings stream 26. It should be noted that the MFT stream20 can be subjected to various preliminary treatments before addition ofthe immobilization chemical 24, such as dilution, coarse debrispre-screening, pre-shearing, thinning and/or chemical treatments toalter certain chemical properties of the MFT stream. The pre-treatedtailings stream 26 is then combined with a polymer flocculant 28, whichcan be added in-line via a co-annular injector. The polymer flocculant28 can be added so as to rapidly disperse into the tailings, forming aflocculating tailings material 30. The flocculating tailings material 30can then be subjected to shear conditioning in order to develop aflocculated material 32 suitable for dewatering.

In some implementations, as illustrated in FIG. 1a , the flocculatingtailings material 30 is subjected to pipeline conditioning 34, which canbe the only conditioning that causes the flocculated material 32 toattain a state in which release water readily separates and flows awayfrom the flocs. Alternatively, other shear mechanisms can be provided.The flocculated material 32 can then be dewatered. FIG. 1a illustrates ascenario where the dewatering includes depositing the flocculatedmaterial 32 onto a sub-aerial DDA 36, which can be a beach or builtusing earthwork techniques. Each DDA 36 can have a deposition regionthat has a sloped base to facilitate release water flowing away from thedeposited material and promote such rapid separation of the releasewater from the flocs.

Still referring to FIG. 1a , over time the structure and operation ofthe DDAs 36 can be managed such that a PASS 38 is formed. The PASS 38includes containment structures 40 for containing the material, a watercap 42, and a solids-rich stratum 44 below a water cap. During formationof the PASS 38, the water cap 42 results from the dewatering of thetreated material. The release water separating from the flocs can be theprimary source of water for the water cap 42 such that the quality ofthe water in the water cap is directly related to the immobilization ofCoCs. It is also possible to add fresh water or another source of waterinto the PASS as it is forming such that the water cap includes waterfrom sources other than the pore water of the tailings. The solids-richstratum includes flocculated solids as well as the immobilized CoCs,which can include bitumen-clay complexes, insolubilized surfactants(e.g., naphthenic acids), insolubilized metals (e.g., arsenic andselenium) and thus inhibits migration of the CoCs into the water cap orwater column. Once the PASS 38 is substantially formed, a fresh waterstream 46 can be added to the PASS and an outlet water stream can bewithdrawn from the PASS, so as to create a flow-through with the watercap 42 in order to maintain the water level and/or gradually reducecertain CoC levels to facilitate supporting freshwater plants and/orphytoplankton. In some implementations, the PASS 38 can be formed byexpelling treated tailings therein for a period of time (e.g., 20 years)in order to fill the PASS to a desired level. During this formationperiod, the water cap 42 can be substantially composed of tailings porewater that has separated out, as well as precipitation and optionallysome other water sources that can be used to account for evaporation.Then, after the formation period (e.g., 20 years), water flow-through isimplemented. The water flow-through can include connecting the PASS 38with existing waterways. The water flow-through provides certain inletand outlet flows of water into and out from the water cap, and graduallyreduces salt levels in the water cap. The water flow-through can beprovided such that the water cap has a certain salt content below athreshold in a predetermined period of time (e.g., below a desired valuewithin 10 years after initiating the flow-through), and salt levels canbe monitored in the water cap, the inlet flow and the outlet flow.

A recycle water stream 48 can be withdrawn from the PASS for recyclingpurposes. In addition, recycle water 48 is withdrawn from the water cap42 and can be supplied to various processing units, e.g., as polymersolution make-up water 50 and water 52 for use in extraction operations54.

Referring now to FIG. 1b , the flocculated material 32 can be suppliedto an SLS 56 instead of a DDA for the main dewatering step. The SLS 56can be various different types of separators. The SLS 56 produces awater stream 58 and a solids-enriched stream 60. In someimplementations, the immobilization chemical can be added upstream ofthe SLS 56, as stream 24 for example. In other implementations, adownstream immobilization chemical stream 62 can be added into thesolids-enriched stream 60, to produce a depositable tailings material 64that can be deposited into a DDA 36. It should also be noted that theimmobilization chemical can be added at both upstream and downstreampoints (e.g., streams 24 and 62). In the scenario illustrated in FIG. 1b, the DDA 36 can be managed such that over time a PASS 38 is formed. Dueto the upstream separation of water 58 in the SLS 56, the water cap 42of the PASS in the ex situ dewatering scenario can be thinner than thatof the in situ scenario. Indeed, in the ex situ scenario, a portion ofthe release water, which can be the primary source of water for thewater cap 42, is withdrawn from the solid-liquid separator as recyclewater 58, thereby reducing the water level of the water cap 42 incomparison to the in situ scenario. Depending on a desired water capdepth, water from other sources can be added to the water cap in the exsitu implementation if there is insufficient water from the remainingtailings pore water.

Turning now to FIGS. 2a to 2e , there are several potential processimplementations for effecting contaminant immobilization as well aspolymer flocculation of suspended solids present in the thick finetailings. In general, chemical immobilization and polymer flocculationcan be effected at different points in the process and by usingdifferent chemical addition approaches.

Referring to FIG. 2a , the MFT stream 20 can be combined with theimmobilization chemical 24 to produce the pre-treated tailings 26, whichis then combined with the polymer flocculant 28 so that a flocculatedtailings material 32 is produced and then subjected to dewatering 66.The dewatering step 66 results in a water stream 68 and asolids-enriched stream 70. It can be noted that the scenario of FIG. 2ais a generalized version of the process similar to that of FIGS. 1a and1b insofar as the immobilization chemical 24 is added to the thick finetailings prior to the flocculant 28.

Referring to FIG. 2b , the immobilization chemical 24 and the flocculant28 are added simultaneously into the MFT 20. The resulting flocculatedtailings material 32 is then supplying to the dewatering step 66. Theco-addition of the immobilization chemical 24 and flocculant 28 can bedone by introducing the two additives via a single addition line orinjector, or by introducing the two additives via separate lines orinjectors at a single point of the MFT flow 20 such that the twoadditives undergo mixing and reaction with the MFT at substantially thesame time.

Referring to FIG. 2c , the MFT stream 20 can be subjected to chemicalimmobilization and polymer flocculation by introducing a single additive72 that has both immobilization groups and polymer flocculation groups.For example, a calcium-based anionic polymer flocculant, includingcalcium cation groups and polymer flocculant groups, could be used toenable both chemical immobilization and polymer flocculation. Polymerflocculants based on multivalent cations instead of monovalent cations,such as sodium, can provide the additional immobilization functionality.The anionicity, calcium content, molecular weight, mixing properties,and other polymer properties can be adapted according to thecharacteristics of the thick fine tailings to obtain desiredimmobilization and flocculation functionalities. Thus, in someimplementations, a single additive that includes a multivalent cationand an anionic polymer can be used. It should be noted that suchadditives could be introduced as part of an aqueous solution where theadditive is fully dissolved, for example.

Referring to FIG. 2d , the MFT stream 20 can first be subjected toflocculation to produce a flocculation stream 74 that is then subjectedto chemical immobilization by addition of a downstream immobilizationchemical 76, thereby producing a treated tailings stream 78 which can besupplied to the dewatering step 66. In such scenarios, shear and mixingimparted to the tailings between the flocculant addition and thedewatering can be adapted to provide suitable shear to flocculate thetailings, mix the immobilization chemical to enable the desiredinsolubilization and immobilization reactions, while avoidingovershearing the flocs.

Referring now to FIG. 2e , the MFT stream 20 can first be subjected toflocculation to produce a flocculation stream 74 that is then subjectedto dewatering 66 to produce the water stream 58 and the solids-enrichedstream 60. This scenario is similar to that illustrated in FIG. 1binsofar as a dewatering step 66 (e.g., using an SLS 56 as in FIG. 1b )is performed prior to addition of downstream immobilization chemical 62.Thus, the solids-enriched stream 60 can be subjected to downstreamimmobilization prior to disposal or further treatment of the resultingsolids-rich stream 80 (e.g., further dewatering such as via beaching ordeposition into the PASS). In addition, the water stream 58 can also besubjected to an immobilization treatment by addition of animmobilization chemical stream 82 to produce a treated water stream 84for recycling or deposition into a holding tank, pond, or as part of thewater cap of the PASS. The immobilization chemical stream 82 added tothe water stream 58 can include the same or different compounds and canhave the same or different concentration profile as the immobilizationchemical 62 added to the solids-enriched stream 60. In someimplementations, the immobilization chemical streams 62 and 82 areprepared or obtained from a common chemical source 86 and can beformulated differently for their respective applications.

It should be noted that various other scenarios beyond those illustratedin FIGS. 2a to 2e are possible in order to subject MFT and/or itsderivative streams to both chemical immobilization and polymerflocculation. The process implementation can be selected depending onvarious factors, such as the characteristics of the thick fine tailingsand its CoCs, the properties of the immobilization chemical and polymerflocculant in terms of reactivity and mixing with the tailings (e.g.,dewatering device or via deposition, weather, deposition variables suchas lift thickness and surface slopes), make-up water chemistry, pipelineconfigurations, and deposition or PASS capacity.

It should be noted that the techniques described herein can be used totreat MFT derived from oil sands extraction operations as well asvarious other thick fine tailings or slurries that include CoCs such assurfactants, metal compounds and/or hydrocarbons or other compoundsimmiscible in the water phase of the slurries. Whether applied to oilsands MFT or other types of MFT or thick fine tailings, variousimplementations described herein enable effective and efficientconversion of the thick fine tailings into a viable aquatic landform andfacilitates permanent storage of thick fine tailings in a reclaimedlandscape. In addition, in some implementations, a number of operationaland environmental compliance constraints can be dealt with such asfacilitating large scale storage of legacy and newly generated finetailings in a permanent aquatic landform that is ready for reclamationwithin a relatively short timeframe (e.g., 10 years) from the end ofmine life, while enabling efficient overall tailings management.

Experimentation, Results & Calculations

Various experiments and calculations were conducted to assess chemicalimmobilization compounds, flocculation, and other process parametersrelated to treating and dewatering MFT.

Chemical Immobilization

Several multivalent salts were evaluated to assess reduction of CoCs inthe release water to levels dictated by performance metrics. Chemicalstested include alum (Al₂(SO₄)₃.14H₂O), gypsum (CaSO₄.2H₂O), iron (II)sulphate (FeSO₄ and also referred to as ferrous sulphate), iron (III)sulphate (Fe₂(SO₄)₃ and also referred to as ferric sulphate) and lime(Ca(OH)₂).

FIG. 3 is a graph of relative removal efficiency in which immobilizationseveral chemicals were tested at different concentrations and projectedup to their saturation limits. FIG. 3 shows that alum was the mostefficient chemical at removing the CoC of arsenic, selenium andnaphthenic acids. Gypsum was also efficient at reducing total suspendedsolids (TSS) and removing bitumen at high concentrations, but was lesseffective in reducing naphthenic acids significantly. Given that gypsumcan be produced on site at certain plants, such as an oil sandsprocessing plant, both alum and gypsum were considered as preferredcandidates for additional study.

Two sets of experiments were conducted to assess impacts of alum andgypsum on the release water. First, different chemical dosages wereadded to undiluted MFT with a solids content of about 38 wt %,homogenized and the entire suspension centrifuged for chemical analysisof the concentrate. The second set of tests was conducted by addingequivalent dosages (on a water basis) to the same MFT diluted withprocess effluent water (PEW) down to about 3 wt %. These diluted MFTsamples were placed in settling columns and allowed to settle for 24 hrsprior to decanting the water for chemical analysis.

The MFT pore water and PEW were tested to determine concentrations ofcertain components. For the particular set of tests, it was observedthat naphthenic acid concentrations appeared uniform between the MFTpore water and the PEW that were used, and that there was a differencebetween other CoCs (arsenic and selenium) between MFT pore water and thePEW. Thus, when PEW is used for dilution of the MFT and/or preparationof flocculant solution, it should be noted that potential differencesand variations in water compositions can influence the immobilizationand flocculation and, consequently, the dosages of the additives can beadapted accordingly. In addition, implementation of the process caninclude a step of determining by measurement or calculation acontaminant concentration in the tailings pore water and/or the PEW orother water source used to add the immobilization chemical andflocculant, in order to control the immobilization and flocculationsteps (e.g., chemical dosages).

Alum

A summary of the effectiveness of alum at removing CoCs from the MFTpore water is presented in FIGS. 4a and 4b for both the diluted andundiluted MFT. The CoC in these tests were naphthenic acids, arsenic,selenium and TSS. Regardless of dilution, to bring CoC levels within theregulatory criteria, naphthenic acid required the most alum (>2500 ppm),while the other CoCs were removed at lower alum concentrations.

The lower arsenic reduction with higher alum concentration for theundiluted MFT can have been due to inadequate mixing at the higher alumdosages (duplicate errors were >50%). Typically, alum is hydrolyzed intoAl(OH)^(+(1,2,4)) within approximately one second where the hydrolysisspecies neutralize the charge on clay particles. At high alum doses andslower dispersion or mixing times, aluminum hydroxide precipitate can beformed and, in turn, can promote sweep flocculation. Given that thecharge neutralization is the primary intent of alum addition, rapidhigh-shear mixing should be implemented to facilitate consistentperformance.

The removal of bitumen from the water column was visually observed tocoincide with TSS removal (about 4.5 meq/L or 1.5 mM Al³⁺). While it canbe desirable to add enough alum to lower the naphthenic acid below 1ppm, increasing alum can also increase the release water conductivityand calcium content in the release water. FIG. 5 illustrates an increasein release water conductivity and calcium content with alum addition.Note that the solubility limit of alum in water at room temperature isabout 36 wt %. Calcium content in the release water can be relevant forvarious reasons, particularly when the water is recycled into extractionoperations. For example, when the water is reused in extractionoperations and is heated using heat exchangers in a hot process watercircuit, the heat exchangers can have certain calcium content limits(e.g., can only tolerate a maximum of about 30 ppm calcium to preventscaling at design conditions or capacity) which can depend on the use ofanti-scaling compounds for example. The maximum alum concentration canbe provided based on the calcium concentrations of the waters (MFT porewater, MFT dilution water and/or polymer solution water), and freshwater can be used for one or more of the water streams added to theprocess. For example, considering fresh water for dilution, the optimumalum concentration can be selected.

Gypsum

FIGS. 6a and 6b show the impact of gypsum on the residual CoC in therelease water, illustrating the efficiency of gypsum at removing CoCsfrom MFT pore water (the open symbols are the performance targets). Inthe diluted MFT tests, gypsum immobilized the CoCs although not to thesame degree as alum. TSS was removed at above 1000 ppm gypsum (about 12meq/L or 6 mM Ca²⁺). At saturation, bitumen should also be sequesteredin the sediment. Some data inconsistency was observed in the 38 wt %undiluted MFT tests for As and Se and can be repeated. FIG. 7 shows anincrease in release water conductivity and calcium with gypsum addition.According to water chemistry data, it was found that at certainimmobilization chemical dosages, TSS, bitumen and metals could beadequately removed from the water column using alum or gypsum, and thatnaphthenic acid could be advantageously removed by using alum.

Another set of experiments was conducted to assess the quality ofrelease water after MFT settling for 30 days, after the addition of thefollowing screened immobilization chemicals: alum (Al³⁺), ferricsulphate (Fe³⁺) and sulphuric acid (H⁺). These latter immobilizationchemicals were screened for chemical immobilization because gypsumdosages above around 10 meq/L Ca²⁺ (860 ppm gypsum in water) remove TSSbelow the 25 ppm threshold whereas alum, ferric sulphate and sulfuricacid removes TSS below the threshold at concentrations around 5 meq/L oftheir cation. Under test conditions, only alum and ferric sulphateremoved arsenic to below the regulatory levels and gypsum had minimalarsenic reduction capability at saturation. Alum, ferric sulphate andsulphuric acid also seem to reduce naphthenic acids significantly, whichwould reduce the amount of fresh water dilution that can be required atclosure of the PASS to safe levels that will ensure a self-establishmentof aquatic biota or organisms.

A standard batch extraction unit (BEU) was used to simulate effects ofoil sands derived MFT settling after addition of the screenedimmobilization chemicals. Results are presented in FIGS. 16 to 20. Thetests were conducted at 55° C. with significant air sparging for bitumenflotation, and designed to maximize bitumen flotation so that the impactof different chemistries could be evaluated. An oil sand slurry(CWR=0.1) was conditioned at 1200 rpm for 20 minutes to ensure maximumbitumen liberation from sand grains. After conditioning, theimmobilization chemical was added and mixed for 1 minute. Flood water(process water) was subsequently added and the mixing reduced to 400 rpmto ensure laminar flow. Air was added to the 1-L volume at approximately7 mls/min while mixing for 10 minutes (primary flotation stage). Thebitumen froth was collected after primary flotation followed by anotherround of mixing and air sparging for 5 minutes to collect the secondaryfroth. The flood water addition is expected to mimic bitumen flotationpotential at the water cap-sediment interface during fresh waterdilution or pond turnover. It should be noted that the test conditionsrepresent a worst-case scenario for bitumen sequestration. FIGS. 16 to20 show that all three acidic immobilization chemicals were effective atsignificantly reducing the organic and metal CoCs. Dosage levels below10 meq/L Al³⁺ can be tolerated for alum, ferric sulphate and sulphuricacid.

Pipeline Mixing

Impact of mixing intensity and time on pH and rheology of the coagulatedthick fine tailings was assessed as follows.

Impact of Mixing Intensity and Time on pH

A series of experiments were conducted on two MFT types (CWR of 0.2 and0.35). The tests were conducted with an alum dosage of 950 mg/L of MFTwater and different mixer rpms. A pH reduction is expected when alum isadded to MFT because alum is supplied in a sulfuric acid solution.However, the experiments were performed particularly to assess howrapidly the pH would buffer back to the equilibrium pH of the MFT. Itshould be noted that the time needed for pH bounce back (within secondsor minutes) can impact pipeline hydraulics as well as polymer flocculantdosage or shear sensitivity of the treated MFT (coagulated andflocculated).

FIG. 23 shows the impact of mixing time and intensity on pH changes ofthe coagulated MFT (which can also be referred to more generally aspre-treated MFT). In general, the pH drops rapidly as soon as alum isadded and bounces back slowly over time, and more rapidly as the mixingintensity increases. The curves were noted to collapse to a criticalmixing value of the mixer (K_(c)) given below and plotted in FIG. 24.

$K_{c} = \frac{N^{2}D^{4}}{V/t}$

N—impeller rotational speed (rps)D—Impeller diameter (m)V—Liquid volume (m3)t—Mixing time (s)

It should be noted that experimentation was conducted in an open vesseland therefore, the impact of CO₂ equilibration with air was unaccountedfor. Iron and calcium carbonates in MFT are expected to dissolve withalum addition with the production of CO₂, which remain dissolved in aclosed system but dissipated in the open system during mixingexperimentation.

Impact of Mixing Intensity and Time on Rheology

A series of experiments was conducted on two MFT types (CWR of 0.2 and0.3) for a mixer speed of 425 rpm and different alum dosages. Resultsare provided in FIGS. 25 and 26.

It should be noted that the rheology response is dependent on the alumdosage. The peak yield stress increases by up to 10 times with alumaddition and coagulated MFT exhibits significantly higher thixotropicbehaviour under constant shear rate as the alum dosage increases.

Another series of experiments was conducted on one type of MFT (CWR of0.35) with alum dosage of 950 ppm and different mixer rpms. Results areprovided in FIGS. 27 and 28. Similar to the pH effect on mixing, therheology of the coagulated MFT also changes with mixing duration andintensity (FIG. 27) and can be described by the mixer critical value(FIG. 28). FIGS. 27 and 28 show a significant variation in the rheologyof coagulated MFT in a timescale within the expected residence time inthe pipeline section between coagulation stage and deposition stage.

Immobilization Chemical to Flocculant Injection Distance (In SituOperation)

A series of experiments was conducted with coagulated MFT of CWR from0.1 to 0.35 in a 6″-diameter vessel, with a 5″ by 1″ paddle mixer, toassess the impact of immobilization chemical to flocculant injectiondistance on performance targets including water clarity and 28-day CWR.The tests used a total volume of about 750 ml, which included thecombined volume of MFT, polymer solution and immobilization chemicalsolution.

Dewatering Performance of Low Shear Coagulated MFT

FIGS. 29 and 30 show an example of performance summary for release waterquality and 28-day CWR for coagulated MFT with feed CWR of 0.35 andexposed to a low-shear during coagulation and prior to flocculation.Water clarity of “3” indicates very low suspended solids and “1” is verycloudy. The following could be concluded from the series of experiments:

-   -   the water clarity degrades with polymer overdose. For both feed        CWRs, water clarity begins to degrade above approximately 2000        g/T of clay, for an alum dosage of 950 mg/L of water;    -   the polymer dosage at which water clarity degradation starts is        dependent on the alum dosage (on a clay basis). Higher alum        dosage (g/T of clay) will tolerate more polymer flocculant        before water clarity is impacted. While the alum dose on a water        basis was 950 mg/L of water in MFT, the alum dosage on clays        vary. Alum dosage on a clay basis was 9500 g/T for 0.1 CWR, 4750        g/T for 0.2 CWR, and 2714 g/T for 0.35 CWR;    -   optimum polymer dosage for the low-shear coagulated MFT, defined        as the highest 28-day CWR given high water clarity (3 on a 1-3        scale), varied between 2200 and 2800 g/T clay for CWR of 0.1 to        0.35; and    -   at the optimum polymer dosage, deleterious impact of the        coagulated and flocculated MFT mixing intensity on water clarity        and 28-d CWR is minimal between 462 and 9508 kJ/m³.

Dewatering Performance of High Shear Coagulated MFT

FIGS. 31 and 32 show an example of performance summary for release waterquality and 28-day CWR for coagulated MFT with feed CWR of 0.35 andexposed to a high-shear during coagulation and prior to flocculation.The following could be concluded from the series of experiments:

-   -   the polymer overdose state is reached quicker for the high shear        MFT than the low-shear MFT. Similar to the low-shear MFT, the        water clarity degrades rapidly with polymer overdose. For both        feed CWRs, water clarity begins to degrade above approximately        1500 g/T of clay, for an alum dosage of 950 mg/L of water;    -   the optimum polymer dosage for the high-shear coagulated MFT,        defined as the highest 28-d CWR given high water clarity (3 on a        1-3 scale), varied between 1000 and 1500 g/T clay for CWR of 0.1        to 0.35; and    -   at the optimum polymer dosage (1000-1500 g/T clay), the impact        of coagulated and flocculated MFT mixing intensity on water        clarity and 28-d CWR is also minimal between 462 and 9508 kJ/m³.

FIG. 33 shows the settling profile expected when an optimum polymerdosage is added to coagulated MFT regardless of the coagulated MFTmixing time. While the initial settling rates are different, thesettling profile follows a similar trend after a few weeks of settling.Therefore, considering that the rise rate expected at the PASS can beapproximately 10 m per annum, self-weight consolidation can be expectedto drive the annual CWR to at least 0.65.

The following conclusions can be derived from the above experiments:

The polymer injection can be performed after addition of theimmobilization chemical such that mixing is within a critical mixingrange. For impeller mixers, such critical mixing can correspond to(K_(c)) of 20 to 12,000. At the design alum dosages between 950 and 1200ppm, the optimum polymer dosage decreases as the immobilization chemicalto flocculant injection distance or K_(c) increases. For example, theoptimum dosage for coagulated MFT with 0.35 CWR mixed at a K_(c), of 20is approximately 2800 g/T of clay, while mixing at K_(c) of 12,000requires a polymer flocculant dosage of approximately 1400 g/T of clay.

For a given flocculant injector design and MFT, dosed between 950 and1200 ppm alum, the polymer flocculant dosage can vary by as much as 20%between MFT with a CWR of 0.1 and 0.35. Once the mixing distance betweencoagulation and flocculation is fixed, the polymer flocculant dosage perm³ of coagulated MFT is dependent on the coagulated MFT solids volumefraction (or CWR) and the alum dosage.

At the optimum polymer dosage, and treated MFT conditioning andconveyance energies tested (up to 9500 kJ/m³), the deposited materialmeets the water clarity criteria (<25 ppm TSS) and CWR>0.65 within ayear. The 9500 kJ/m³ tested is equivalent to an average shear rate of150 s⁻¹ for 30 minutes after flocculant addition to coagulated MFT. Thisapproximates to a maximum of 6 km in a 20″ pipeline at an average linevelocity of 3.5 m/s that can be used in large scale operations.

Flocculation and Dewatering (In Situ Dewatering)

On a bench scale, flocculation and in-line dewatering processes wereevaluated concurrently as it has been found that maximum dewatering canbe coupled to optimum flocculation. The flocculation polymer selectionis based on direct experience from thin lift drying technology in whichpolymeric flocculants react with minerals in the tailings through anumber of mechanisms to remove minerals from the tailings suspension(e.g., MFT) by forming aggregates (flocs). However, in addition to thepolymer flocculant properties, the extent of interaction between theflocculant and the mineral particles is also dependent on the thick finetailings properties (e.g., particle size and shapes, pore waterchemistry, rheology, and the slurry hydrodynamic condition duringpolymer injection). In the in situ dewatering option where theimmobilization chemical is added before the flocculant, alum and gypsumcan act as coagulants that destabilize the particles in the thick finetailings through double-layer compression and modify the pore waterchemistry. These effects can change the nature of theflocculant-particle interaction relative to a process utilizing onlypolymer flocculant.

Polymer Flocculant Screening

Screening tests were conducted to narrow down potential flocculants forMFT either untreated or previously coagulated with gypsum and alum.Three sodium-based anionic polyacrylamides (aPAMs) were tested: polymerA; polymer B; and polymer C. In addition, a deep deposit specialtychemical (DDSC) was tested, as well as a calcium-based anionicpolyacrylamide (polymer D). A combination of alum and sodium aluminatewas also tested.

Dewatering efficiency (24 hour CWR) was used as a screening parameter.At each immobilization chemical dosage (typically between 0 and ˜10meq/L for alum and gypsum) the optimum polymer dosage was determined,followed by determination of the 24 hour CWR, the suspended solids andwater chemistry of release water. Selection was based on the lowestimmobilization chemical dosage for maximum 24 hour CWR meetingoperational criteria of 0.65. The quality of the water recovered fromthe 24-hour CWR (sieved through a 325-mesh screen) was used to representthe expected water quality at closure. The total suspended solids in thepore water can be at most 25 ppm, and the suspended bitumen on water capof approximately 0 ppm.

Given the differences in the chemistry of the polymers, it was foundthat each polymer flocculant benefited from mixing control to maximizedewatering efficiency. The four aPAMs (polymers A to D) performed wellin the screening tests and the three sodium-based aPAMs (polymers A toC) were further evaluated with respect to flocculation.

Tests were conducted with immobilization chemical addition either beforeor after flocculant addition. It was found that adding theimmobilization chemical (which can also be referred to as coagulanthere) prior to the flocculant facilitated achieving advantageous CWRlevel and TSS reduction. When the MFT was flocculated prior to addingthe immobilization chemical in the in situ dewatering process, theresultant CWR was found to be notably reduced at the dosages requiredfor low TSS in the water phase.

Tests generally showed that MFT with CWR of at most 0.2 can require ahigher immobilization chemical dosage demand (but lower polymer dosagedemand), while MFT with CWR of at least 0.35 will require lowerimmobilization chemical dosage demand but higher polymer dosage demand.

Flocculent Dosages for Alum- or Gypsum-Treated MFT

Using the same mixing parameters, the optimum dosages for flocculation(measured by the 24 hour CWR) were evaluated for the aPAM polymers A, Band C. As shown in FIGS. 8a to 8c , the polymer flocculant dosages foroptimum flocculation and maximum dewatering tended to increase with alumor gypsum additions for all three aPAMs. In all cases, approximately 0.3mg/kg-clay to 0.6 mg/kg-clay of additional polymer was required per ppmof alum addition, and slightly less polymer increase for gypsumadditions. It should be noted that improvement of the mixing parametersfor the immobilization pre-treated MFT should modify the polymer dosagerelative to a baseline no-immobilization chemical scenario. FIGS. 12aand 12b show polymer dosage versus gypsum dosage for polymers B and Arespectively.

Impact of Alum on MFT Dewatering Performance

Extensive investigation was conducted on the dewatering potential ofalum-treated MFT at the respective optimum polymer dosages. Again, themixing parameters were fixed at the optimum for the no-immobilizationchemical case and could be enhanced. FIGS. 9a and 9b illustrate theimpact of alum addition on dewatering potential and polymer dosagerespectively. Below about 950 ppm alum (about 9.5 meq/L Al³⁺), the24-hour CWR was similar to the no-immobilization chemical case (baselinecase) and the clay capture was better for all three aPAMs. Within thisrange, polymers B and C performed significantly better than polymer A,albeit at higher polymer dosages. At lower alum dosages, polymer C alsorequired the lowest dosage for maximum water release. Referring to FIGS.9a and 9b , the shaded area (left) is considered similar to the baselinecase without immobilization chemical addition, while the unshaded area(right) is considered worse than the baseline case.

To achieve the desired CWR performance in the treatment of these MFTsamples, it was found that the alum dosage should not exceedapproximately 1000 ppm. At 950 ppm of alum, the TSS, bitumen and metalsshould meet the performance criteria, and naphthenic acid would beapproximately 60% remediated to target levels. To confirm thegeochemical performance, the release waters collected after flocculationand 24-hour dewatering were analyzed in a similar fashion to theprocedure to obtain the data in FIGS. 4a and 4b . Details of the releasewater chemistry at alum dosages up to about 1750 ppm were obtained. Thegeochemical markers at 360 and 950 ppm alum were also obtained.

Referring to FIG. 9a , the CWR at 360 ppm alum is notably higher thanthe baseline (0 ppm alum) and at 950 ppm alum; however, the TSS andresidual bitumen in the release water were found to be higher thandesired. With polymer C in particular, the naphthenic acid reduction wasapproximately 40%. An alum dosage around a maximum CWR (e.g., 360 ppm inFIG. 9a ) could be combined with saturated gypsum to maintain or improvethe desired CWR while reducing the naphthenic acid concentration.Overall, addition of polymer flocculant appears to have reduced some ofthe immobilization benefits provided by alum. For example, in FIG. 4most of the TSS is removed at about 470 ppm alum; but significantresidual solids remained at 867 ppm alum especially when used withpolymer C. It was also found that naphthenic acids and calcium werelargely unaffected by the polymer.

The following Table A provides some release water chemistry results ofMFT after flocculation and treatment with 360 ppm and 950 ppm alum:

TABLE A Base Case (polymers B Polymer B Polymer C and C) 360 ppm 950 ppm360 ppm 950 ppm 24 h CWR 0.47 (± 0.04) 0.54 (± 0.04) 0.46 (± 0.01) 0.50(± 0.01) 0.46 (± 0.02) TSS (ppm) 3836 (± 509) 2312 0 1947 0 Dissolvedsalts 3730 3920 4130 3720 4177 (conductivity) (μS/cm) Bitumen in water −− 0 − 0 (ppm) Naphthenic Acid 26 20 12 15 12 (ppm) Calcium (ppm) 10 1223 14 23

While a higher alum dosage (>10 meq/L Al³⁺) can improve the releasewater clarity, it can result in levels of dissolved salts (includingcalcium and sulphate) higher than operational and closure threshold.Increasing alum dosage was found to increase the dynamic yield stressand viscosity of the MFT, and therefore the mixing intensity requiredfor inline flocculation. Optionally, polymers that can achieve theoperational and closure threshold at lower alum dosages can be chosen.Optionally, ferric sulphate and sulfuric acid can be used as alternativeimmobilization chemicals to alum.

Impact of Gypsum on MFT Dewatering Performance

FIGS. 10a and 10b shows the impact of gypsum addition on the dewateringpotential and optimum polymer dosage for MFT flocculated with the threeaPAMs. For all the polymers, the 24 hour CWR increased with gypsumconcentration up until saturation at about 2500 ppm. The polymer dosageis also notably higher with gypsum additions, but the increase would bereduced with enhanced mixing of the additives. Overall, polymer Cdisplayed the best performance as the tested conditions with gypsum.Geochemical markers for saturated gypsum with polymers B and C are givenin Table B:

TABLE B Base Case (polymers B Polymer B Polymer C and C) 1250 ppm 2500ppm 1250 ppm 2500 ppm 24 h CWR 0.47 (± 0.04) 0.50 (± 0.03) 0.50 (± 0.02)0.48 (± 0.02) 0.51 (± 0.02) TSS (ppm) 3836 (± 509) 691 0 636 0 Dissolvedsalts 3730 4290 5010 4740 5260 (conductivity) (μS/cm) Bitumen in water −− 0 − 0 (ppm) Naphthenic Acid 26 21 19 23 20 (ppm) Calcium (ppm) 10 3377 52 113

The 24 hour CWR at saturated gypsum addition (2500 ppm) was consistentlyhigher than the base case. Also, at these dosage levels, the TSS andbitumen are removed from suspension. Similar to the results shown inFIGS. 6a, 6b and 7, there is notably lower naphthenic acid removal bysaturated gypsum solution from the release water compared to alum at 360ppm or 950 ppm. The residual conductivity will also lead to higherdilution requirements at closure compared to alum or the base case.

Dewatering Optimization at 950 (±100) ppm Alum

Based on field experience in flocculation and dewatering operations ofMFT as well as investigations into fundamentals of chemical mixing, thepolymer dosage can be minimized and 24 hour CWR maximized throughoptimal mixing at mesoscale, i.e., the scale of the bulk of clay mineralparticles in a dispersed slurry (between 0.1 μm and 1 μm equivalentspherical diameter). Addition of alum or gypsum changes theclay-aggregate scales and would benefit from optimization. To determinethe required range of mixing on a bench scale, an optimized fractionalfactorial experiment (108) was conducted at two immobilization chemicaldosages (0 ppm and 950 ppm alum), three mixer rotations per minute (RPM)(300 RPM (base case), 600 RPM and 900 RPM), three polymer injectionrates, and two MFT clay-to-water ratios (0.25 CWR and 0.35 CWR).Polymers B and C, which had given the best results according to previoustesting, were selected for this stage of testing.

The polymer dosage was optimized at each test condition. FIGS. 11a and11b show the results for polymer C with and without alum pre-treatment.The mixer was optimized for the base case (0 ppm alum) at 300 RPM withthe lowest optimum polymer dosage (about 1000 mg/kg clay) and maximumwater release (CWR of about 0.45). Dewatering became progressively worseat 600 RPM and 900 RPM with associated increases in optimum polymerdosage. The alum-treated MFT required higher pre-shear prior to polymeraddition, and showed a maximum CWR and minimum dosage at 900 RPM.

It is noted that the mixing could be provided based on the particularimmobilization chemical and polymer flocculant used in the process inorder to enable greater dewatering and lower polymer dosagesparticularly for the larger scale operations. Mixing design and controlcould include, for example, special injector designs and/or dilutioncontrol.

Characteristics of PASS Performance Via In Situ Dewatering OperationalPerformance

Certain aspects of the operational performance of the PASS are providedbelow.

Volume Reduction

The deposited or discharged treated MFT is expected to be at a steadystate CWR≥0.65 during operations and continue to densify and consolidateafter the end of mine life (EOML). The consolidation rate can bedetermined via additional bench scale studies and/or monitoring of afield prototype. Based on bench scale studies, the use of 950 ppm alumor saturated gypsum in the MFT slurry did not reduce the CWR achievablein the field relative to a base case in which no immobilization chemicalis used.

Recycle Water Quality

At 950 ppm alum, the unmitigated residual calcium in the recycle waterwould be within the desired operating envelope for certain heatexchangers in which anti-scaling agents are used. For gypsum-treatedMFT, the residual calcium is about 100 ppm and would benefit fromadditional mitigation within the operating envelope for certain heatexchangers. The calcium concentration in the release water and/or capwater can be monitored and calcium reduction can be implementeddepending on the equipment (e.g., heat exchanger) or processrequirements to which the water is recycled. Calcium levels can bereduced by dilution with other water streams, exchanging for sodium onclay surfaces, and/or precipitating as calcium carbonate prior toincorporation into certain equipment or unit operation of the extractionprocess.

In addition, an unmitigated increase in the total dissolved salts andreduction in bicarbonate of the recycled water could have a negativeimpact on bitumen recovery. Using water chemistry data, the bitumenrecovery loss due to increased salt levels was estimated to be about 0.5wt % for 950 ppm alum and about 2 wt % for MFT treated with saturatedgypsum. The bitumen recovery losses can also become progressivelygreater with increasing clay content in the oil sands ore.

Closure Performance

Certain aspects of the closure performance of the PASS are providedbelow.

Suspended Solids

Without alum or gypsum addition, the water cap of the PASS is expectedto contain significant amounts of suspended solids, which are currentlydifficult to mitigate at large scales. Suspended solids in the watercolumn would also be exacerbated during the spring and fall pondturnover events. At 950 ppm alum and 2500 ppm gypsum, the TSS isexpected to be close to zero. Pond turnover would generate suspendedsolids during the event, but would settle fairly rapidly depending onthe aggregate sizes of the aggregated solids.

After closure, fresh water dilution provided would change the chemistryof the water cap of the PASS. Negative impacts of the chemistry changeon suspended solids could be mitigated by controlling the dilution water(e.g., fresh or surface run off rather than process water with highbicarbonate content). In addition, capping the sediment layer with acoarse material (e.g., coke or sand) could mitigate againstre-suspension of fine solids or bitumen during pond turnovers. Thecoarse material could be distributed over the water cap (e.g., via anaqueous slurried stream containing the coarse material pumped to thePASS) and the coarse material would then settle by gravity onto thelower layer of sediment. This intermediate layer could be used to capthe mud layer, which is the interface between water and the sediment, atthe end of operation and start of reclamation. For example, coke couldbe slurried through the water cap and would be light enough to stay ontop of the mud layer. The coke layer or another type of intermediatelayer could facilitate minimizing the flux of CoCs between the lowerdeposit and the water cap. Coke could potentially adsorb some of theCoCs. Other particular material could also be used, particular thosethat are porous and have absorptive properties.

Bitumen in Suspension

Bench scale studies suggest that bitumen immobilization within thesediment tracks suspended solids removal. This can be at least partlydue to negatively charged bitumen surface being able to coagulate withcations similar to the negatively charged clay surfaces. Calcium,magnesium or an aluminum hydroxyl complex could bridge destabilized clayparticles to bitumen droplets, thereby chemically immobilizing bitumenwithin the sediment. This mechanism has been observed in primary bitumenextraction where overly high calcium content in the process or oreconnate water can depress flotation of bitumen into the froth layer.

Microbial activity due to increased concentrations of sulphate andpossible availability of easily degradable organic carbon (e.g., fromaPAMs or bitumen light fractions) could generate gas. Gas bubbles canpotentially refloat bitumen droplets into the water column if thebitumen is insufficiently immobilized. However, microbial activityfurther degrades bitumen and promotes mineral adsorption on bitumensurfaces, which, in turn, can inhibit bitumen flotation. Both alum andgypsum at the appropriate dosages should immobilize bitumen through toreclamation and inhibit substantial remobilization or flotation. Theimmobilization chemicals and polymer flocculant can be selected anddosed such that gas-induced floatation of bitumen is inhibited withinthe PASS.

Regulated Metals

Arsenic and selenium are the primary metals in exceedance of fresh waterguidelines for aquatic life for certain example MFT samples under study.Referring to FIGS. 13a and 13b , the dilution evaluation was based onthe pore water chemistry of MFT samples obtained from a particulartailings pond and used in this study and on the process water used forMFT dilution. FIGS. 13a and 13b show the amount of fresh water dilutionto bring the landform release water within the target limits for arsenicand selenium. With no immobilization chemical, approximately 80% freshwater dilution is required compared to 50% for 950 ppm alum and 70% forsaturated gypsum, for example. It should be noted that these levels arederived from the 3 wt % MFT slurry. Lower selenium levels in the MFTpore water suggest that lower or no dilution would be required to bringselenium down to 1 ppb for undiluted cases.

Toxicity and Naphthenic Acid

In some scenarios, certain CoCs or categories of CoCs can be used as aproxy for toxicity. For instance, for certain MFT materials naphthenicacid can be used as proxy for the toxicity. Unlike metals, naphthenicacids degrade at a notable rate (e.g., at about 16% per year in columntests and even more rapidly within years at larger commercial scaleoperations). Referring to FIG. 14, using the lower degradation rates fordesign prudence, ten years after PASS closure the concentration ofnaphthenic acid would be significantly reduced and would require minimaldilution with fresh water. Approximately 70% dilution would be requiredto remediate the saturated gypsum treated PASS landform to targetlevels. Alum treatment would require approximately 50% dilution. Atfaster naphthenic acid degradation rates that have been observed, thenaphthenic acid concentration would be below 1 ppm within only 7 yearswith no immobilization chemical addition. In this regard, “dilution”percentage refers to the percentage fresh water with respect to theoverall water. Thus, for 70% dilution, there is 70% fresh water and 30%from the original process affected water in the tailings. The dilutionpercentage is the volume percentage of fresh water to bring the watercap within target guidelines for a fresh water lake, and is primarilyguided by the salt level which certain immobilization chemicals cannotremediate.

Dissolved Salts

Fresh water dilution is advisable to bring the dissolved salts down tolevels that can support freshwater organisms. The electricalconductivity of 340 μS/cm was used for fresh river water in thisanalysis. At 2000 μS/cm, the release water can support freshwaterplants, and below 1000 μS/cm phytoplankton can be supported. With noimmobilization chemical, 50% and 80% dilutions are required to achievethe freshwater plants and phytoplankton criteria respectively. For alumadditions at 950 ppm, a 60% dilution can be required for freshwaterplants and up to 80% for phytoplankton, while about 70% dilution can berequired to meet the freshwater plants criterion for gypsum, accordingto the example dosages obtained pursuant to the testing describedherein. If, at maximum dilution rates, saturated gypsum treatment is notable to meet the phytoplankton criteria and/or the salt loading in theprocess water and the pore water of the MFT increase during the life ofmine, water treatment can be implemented accordingly.

In summary, according to the studies based on example water and tailingsproperties, a 50% to 60% fresh water dilution of 950 ppm alum treatedlandform would meet geochemical criteria to support freshwater plants,and 80% fresh water dilution would ensure support for all freshwateraquatic organisms within a ten-year timeframe. For gypsum, fresh waterdilution at the maximum 80% would meet all criteria except forfreshwater aquatic organisms. In the corresponding base case, althoughan 80% dilution would meet the criteria for freshwater aquaticorganisms, the suspended solids and bitumen migration in the watercolumn would not be mitigated by fresh water dilution and would have tobe dealt with via other means.

Impacts of Water Chemistry on Dewatering Operations

Studies were conducted to evaluate potential impacts of increasingprocess water ionic strength on MFT drying operations. The ionicstrength increases that were investigated were from NaCl (ore connatewater) and flue gas desulfurization (FGD) gypsum. Other additives,including reverse osmosis reject brine solutions or evaporator feed withhigh organic acids, were also tested.

In these studies, the NaCl or Flue Gas Desulfurization (FGD) gypsumsalts were introduced into the polymer make-up water which was about 10%of the total water in MFT. Manipulating the salt content of the polymermake-up water was operationally less intrusive and offers greaterprocess performance predictability than adding salt directly into theMFT flow. Other additives were also tested. A 0.45% polymer solution wascreated for each additive. Polymer A was used. A dose sweep wasconducted to determine the optimum dose for the MFT sample. Optimallyflocculated MFT was stacked in 2 cm lifts and allowed to drain for 24hrs to determine the initial water release (or net water release) andthe release water chemistry. Evaporation of the lifts was monitored overa week until completely dried.

In terms of the findings, the use of saturated gypsum, reverse osmosisreject brine solutions or evaporator feed with high organic acids didnot significantly impact flocculation of MFT or the release waterchemistry. Increases in PEW TDS to a maximum of about 5500 ppm in futureoperations would not significantly impact flocculation efficiency orrelease water chemistry, although polymer dosage can increase by about10%. For a saturated gypsum make-up water, the optimum polymer demandincreased by 15%. In addition, for polymer make up water saturated withgypsum, adsorption of Ca²⁺ on clays limited the Ca²⁺ in the 24-hourrelease water to below 30 ppm. The Ca²⁺ concentration from recycle waterresulting from the use of a saturated gypsum solution for polymermake-up, should not have a significant impact on pipe scaling or bitumenextraction. Furthermore, the Ca²⁺ appeared to improve the initialevaporation rate of 2 cm lifts. In addition, run off from dried MFT withreverse osmosis brine and evaporator feed had TDS higher than PEW andvaried with the TDS in the polymer water; high gypsum concentrations didnot significantly increase TDS in the runoff; and runoff water qualitycan be better in the field compared to lab work as only exposed surfacesare impacted in field operations.

It was found that salts additives can reduce the maximum drying rate(including sub-aerial deposition cell utilization) determined forexisting MFT drying operations. For FGD gypsum, this would indicate thatlarge amounts of gypsum should not be stored in the dried MFT matrix;and for high NaCl make-up water, a mitigation strategy can beimplemented to reduce NaCl content in the waters (MFT pore water and/orpolymer make-up water) present in the MFT drying process, particularlyas higher NaCl concentrations occur as PEW salts cycle up. Increased TDSin runoff water can also merit mitigation strategy to reduce the impacton recycled water that influences PEW chemistry. A reduction in thegeotechnical stability of the deposit due to salt additions would alsowarrant assessment to reduce potential negative impacts on finalreclamation on closure.

PASS Process Modelling and Experimentation

Additional experimentation and modelling were conducted regarding targetsteady-state CWR of the treated material in the PASS. An exemplarytarget was a CWR of at least 0.65 within one year of discharge into thePASS structure.

Process modelling strategy included evaluation of the parametersinfluencing the dewatering rate and the steady-state CWR. Dewateringrate is considered to vary according to the floc size distribution andthe floc density of the coagulated and flocculated MFT, and thereforeaccording to the CWR of the MFT, the immobilization chemical andflocculant dosage and the shear history. The steady-state CWR isconsidered to vary according to deposit depth (also referred to as totalstress) and floc size distribution and density of the coagulated andflocculated MFT.

The following equation was used to empirically model the CWR as afunction of time with a variable slope.

${CWRt} = {{CWR_{t = 0}} + \frac{\left( {{CWR_{t = \infty}} - {CWR_{t = 0}}} \right)}{\left( {1 + \left( \frac{T_{50}}{T} \right)^{Rate}} \right)}}$

-   -   CWR_(t=0) and T (days) are independent variable    -   CWR_(t=∞) is the final (steady state) CWR    -   T₅₀ is the time to reach 50% of the total strain        (CWR_(t=∞)−CWR_(t=0))    -   Rate is a dimensionless quantity to characterize the relative        “deformation or strain rate”. It is the slope of the logistic        function—a logarithm slope. So, Rate<1 is very rapid initial        settling and >1 is slower initial settling.

The above empirical model resulted from experimentation includingcolumns tests filled with coagulated and flocculated MFT. Theexperimental matrix include varying the initial CWR, cMFT preshear,immobilization chemical and polymer dosages and several levels of cfMFTshear. Each output cfMFT is allowed to settle over a period of severalmonths in columns between 10 cm to 200 cm tall, and the settling profilecontinuous monitored. Once the columns have reached steady state (from afew days to several months depending on the input variables), thesediment layer is sectioned and analyzed for density, clay content andpore water chemistry. Full geochemical and toxicology analyses are alsoconducted on the release water.

Steady-State CWR (CWR_(t=∞))

Major variables influencing steady-state CWR include feed CWR anddeposit height (also referred to as total stress). More precisely,CWR_(t=∞) increases as feed CWR increases (Floc density increases withfeed CWR). In addition, CWR_(t=∞) increases with deposit height (selfweight). Experimentation parameters and results for two columns withrespective feed CWR of 0.35 and 0.2 are reproduced below in Table C andthe modelled CWR reported in FIG. 34.

TABLE C Feed cfMFT CWR_ Column Shear Alum Polymer Column Height RateDosage Dosage Final ID (cm) (1/s) (ppm) (g/T) CWR_(∞) CWR_(t=300 d)0.35_R07 56 12 1200 1600 0.49 0.47 0.35_R07 33 12 1200 1600 0.46 0.450.35_R07 11 12 1200 1600 0.43 0.42  0.2_R15 56 12  950 1400 0.40 0.39 0.2_R15 33 12  950 1400 0.37 0.36  0.2_R15 10 12  950 1400 0.31 0.30

Minor variables influencing steady-state CWR include polymer dosage andshear rate. More precisely, experimentations showed that high polymerdosage and high shear rate reduce CWR_(t=∞). Longer shear durationappears to favor enhanced floc packing efficiency. Experimentationparameters and results are reproduced below in Table D and thecorresponding modelled CWR illustrated in FIG. 35.

TABLE D Column ID R03 R07 R04 R08 Polymer (g/T 3200 1600 3200 1600 clay)Shear Rate 12 12 45 45 (1/s) Total Energy 377 413 1260 709 (kJ/m³)CWR_(300d) 0.44 0.45 0.43 0.46 CWR_(∞) 0.51 0.49 0.48 0.48

Settlement Rate (Rate)

Referring to FIGS. 36 to 38, it has been found that major variablesinfluencing initial settlement rate include polymer dosage, feed CWR,total energy and shear rate. More precisely, the settlement rateincreases as polymer dosage increases (larger floc sizes with morepolymer). Initial settlement rate decreases as feed CWR increases, whichcan likely be a consequence of better flocculation efficiency at lowerCWR. Furthermore, initial settlement rate decreases as total energy andshear rate increase. Total energy can be seen as a combination of shearrate, shear time and coagulated/flocculated MFT (cfMFT) rheology. Bothparameters contribute to smaller aggregate floc sizes.

Time to Reach 50% of the Total Strain (T₅₀)

Major variables influencing the time to reach 50% of the total strain(T₅₀) include polymer dosage, feed CWR and total stress. More precisely,referring to FIG. 39, experimentations showed that T₅₀ increases aspolymer dosage, which is correlated to the rapid initial settlement ratewith increasing polymer dosage. In addition, T₅₀ increases as feed CWRincreases, which is correlated to the slower initial settlement rateobserved with increasing feed CWR. T₅₀ also increases as total stressincreases, as greater self weight translates to a more prolonged strain.Experimentation parameters and results are reproduced below in Table E.

TABLE E Column ID R03 R20 R07 Feed CWR 0.35 0.35 0.35 Height (cm) 55 46*55 cfMFT Shear 13 12 12 rate (1/s) cfMFT Shear 56 56 61 time (min) TotalEnergy 377 329 413 (kJ/m³) Polymer g/T 3200 2000 1600 clay CWR_(∞) 0.510.44 0.49 Rate 0.3 1.0 1.1 T₅₀ (days) 14 11 35 CWR_(t=300 days) 0.440.44 0.47

Floc Size

The average floc size is expected to drive the “initial settlement ordeformation rate”. Referring to FIGS. 40 and 41, major variablesinfluencing the floc size are both the polymer dosage and the totalenergy (or mixing energy) similarly to the initial settlement rate.Unlike the initial settlement rate which is sensitive to the feed CWR,the small negative impact of higher CWR can likely be due to lowerflocculation efficiency at higher CWR in the laboratory test. Furthertests showed that coagulation seems to promote greater resistance tofloc attrition, so positive correlation of immobilization chemicaldosage to floc size is not unexpected.

Shear

Experimentation parameters and results are reproduced below in Table F,and the corresponding average CWR showed on FIGS. 42 to 44. Figures showthat for similar column heights (or self-weight), a higher final CWR isachieved with increasing shear of the coagulated and flocculated MFT andlower immobilization chemical dosage.

TABLE F Column ID R27 R27U R15 R15U R11 R11U Rate 0.35 0.66 0.55 0.570.24 0.61 T₅₀ 145 180 1 3 5 74 (days) CWR_(∞) 0.63 0.51 0.40 0.34 0.440.39 Polymer 1300 1300 1400 1400 2800 2800 g/T clay Alum 0 0 950 950 950950 ppm

FIGS. 45 and 46 show the column profile after 3 months of settling atminimal shear from the bottom to the top of the column, for coagulatedand flocculated MFT and for flocculated MFT. The average CWR seem to bemore impacted by the coagulation than the segregation potential forclays.

1. A process for treating tailings, comprising: adding a flocculant toan in-line flow of material comprising tailings to produce aflocculating material; subjecting the flocculating material to shearconditioning to form a conditioned flocculated material; conveying theconditioned flocculated material to a pit under shear rate and energyconditions that are lower than those of the shear conditioning used toform the conditioned flocculated material; and discharging theconditioned flocculated material into the pit to enable waterseparation.
 2. The process of claim 1, wherein the shear conditioning ispipeline shear conditioning provided to put the conditioned flocculatedmaterial in a water release zone upon discharging into the pit, therebyproducing a water component and a solids-enriched component comprisingflocculated solids.
 3. The process of claim 2, wherein the pipelineshear conditioning is performed to: produce a gel-state material havingincreased yield stress; and then produce the conditioned flocculatedmaterial having an ungelled state and a decreased yield stress comparedto the gel-state material.
 4. The process of claim 2, wherein theconditioned flocculated material being in the water release zone resultsin an initial clay-to-water ratio (CWR) in the solids-enriched componentof at least 0.55 or at least 0.65.
 5. The process of claim 1, whereinthe conveying of the conditioned flocculated material to the pit isperformed under non-turbulent flow conditions.
 6. The process of claim1, further comprising forming a permanent aquatic storage structure(PASS) from the conditioned flocculated material that is discharged inthe pit, the PASS comprising: a water cap formed by the water releasedfrom the conditioned flocculated material; and a consolidatingsolids-rich lower stratum below the water cap, formed by settling andconsolidation of the conditioned flocculated material.
 7. The process ofclaim 1, wherein the in-line flow of material comprises chemicallyimmobilized contaminants of concern.
 8. The process of claim 1, whereinthe flocculant comprises an anionic polymer flocculant.
 9. The processof claim 8, wherein the anionic polymer flocculant comprises asodium-based or calcium-based polyacrylamide-polyacrylate co-polymerwith high molecular weight.
 10. A process for treating fine tailings,comprising: adding in-line a coagulant to a fine tailings flow to causecoagulation and to form a coagulated tailings material flow; addingin-line a flocculant to the coagulated tailings material flow to producea flocculating tailings material flow; subjecting the flocculatingtailings material flow to shear conditioning to produce a conditionedflocculated tailings material; dewatering the conditioned flocculatedtailings material to form: water; and a solid-enriched componentcomprising flocculated solids.
 11. The process of claim 10, wherein theshear conditioning is pipeline shear conditioning that is conducted toincrease a yield stress of the flocculating tailings material flow to amaximum where the flocculating tailings material flow presents gel-likecharacteristics, and then to reduce the yield stress and effect flocbreakdown to form the conditioned flocculated tailings material in awater release zone.
 12. The process of claim 10, further comprisingconveying the conditioned flocculated tailings material under shear rateand energy conditions that are lower than those of the shearconditioning.
 13. The process of claim 12, wherein the conveying of theconditioned flocculated tailings material is performed undernon-turbulent flow conditions.
 14. The process of claim 10, wherein thedewatering comprises: continuously depositing the conditionedflocculated tailings material onto a sub-aerial deposition area to allowan initial water release from the conditioned flocculated tailingsmaterial and to start forming the solids-enriched component.
 15. Theprocess of claim 14, wherein the sub-aerial deposition area is a pit andthe process further comprises forming a permanent aquatic storagestructure (PASS) from the conditioned flocculated tailings material thatis discharged in the pit, the PASS comprising: a water cap formed by thewater released from the conditioned flocculated tailings material; and aconsolidating solids-rich lower stratum below the water cap, formed bysettling and consolidation of the solid-enriched component.
 16. Theprocess of claim 14, wherein the sub-aerial deposition area has a slopedbase to facilitate release water draining from the solids-enrichedcomponent.
 17. The process of claim 16, wherein the sub-aerialdeposition area is a sloped sub-aerial beach and the process furthercomprises forming a thin lift via deposition of the conditionedflocculated tailings material flow to allow water to drain from the thinlift and form the solid-enriched component.
 18. The process of claim 17,wherein the thin lift is a lower thin lift and the process furthercomprises stacking at least one additional thin lift on a top of thelower thin lift once the lower thin lift is dewatered, to form multiplethin lifts.
 19. The process of claim 18, wherein each thin lift is a 2cm lift.
 20. The process of claim 10, comprising further dewatering ofthe solid-enriched component via freeze-thaw mechanism.
 21. The processof claim 10, comprising further dewatering of the solid-enrichedcomponent via evaporation mechanism,
 22. The process of claim 10,comprising further dewatering of the solid-enriched component viapermeation mechanism.
 23. The process of claim 10, wherein theconditioned flocculated tailings material has a target floc size that isgreater than 100 pm upon discharge.
 24. The process of claim 23, whereinthe target floc size is greater than 150 pm.
 25. The process of claim23, wherein the target floc size is greater than 200 pm.
 26. The processof claim 23, wherein the target floc size is greater than 250 pm.